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This  Volume  is  for 
REFERENCE  USE  ONLY 


RADIO  BROADCAST 


VOLUME  XIII 


MAY,    1928,   to  OCTOBER,    1928 


GARDEN  CITY  NEW  YORK 

DOUBLEDAY,    DORAN   &   COMPANY,  INC. 

1928 


.  ;•:• :  ••-.      •••  .-.  •  ^i-: 

*          .•  *.  ••  r-: 

•    •  •  ••*      ••* •    »••• ••  • 


INDEX 

(*Illustrated  Articles.    Editorials  in  Italics) 


PAGE 

*  A  -B-C  Power  Unit  and  One-Stage 
-tV  Amplifier,     An     Interesting     (J. 

George  Uzmann) 145 

*A-Power  Unit  from  Your  Battery 
Charger,  Making  an  (Robert  Burn- 
ham) 137 

*Adapter  for  Long- Wave  Reception,  An 

(W.  H.  Wenstrom) 275 

*Adding  Regeneration  to  Any  Set  (Her- 
bert Grove) 210 

*A11    About    Loud    Speakers    (Joseph 

Morgan) 188 

Allocation.  The  Engineers  Plan  of  .  .  .      132 
*A.    C.    Receiver,    A    Dual    Control 

(Robert  Burnham) 192 

*A.  C.  Screen-Grid  Receiver,  An 37 

*A.  C.  Screen-Grid  Tuner,  A  Two-Tube 

(James  Millen) 349 

*A.  C.  Super-Heterodyne,  A  Flexible 

(Dana  Adams) 39 

Amateur   Bands,    Keep   Commercialism 

Out  of  the 254 

Amateurs  in  the  Ten-Meter  Band 197 

'Amplifier  and  B  Supply,  A  Space- 
Charge  (H.  P.  Manly) 163 

*  Amplifier  and  Power  Supply,  A  Resist- 

ance-Coupled (J.  George  Uzmann).  .     257 
*Amplifier  Power  Unit  for  the  250,  A 

Good  (Howard  Barclay) 141 

*Amplifier,  The  222  Tube  as  an  R.  F. 

(Glenn  H.  Browning) 252 

Annual  Report  of  the  R.  C.  A 11 

Another  Non-Radio  Man  for  the  Com- 
mission   131 

Apparatus,  New.  .  .  35,  85,  139,  227,  284,  372 
*As    the    Broadcaster    Sees    It    (Carl 

Dreher) 42,  102,  161,  219,  267,  352 

*Audio  Combination,  The  Right  (L.  W. 

Hatry) 23 

*Audio    Distortion,    Checking   Up   on 

(G.  F.  Lampkin) 290 

*Audio  Transformer   Design,   A   New 

Principle  in  (Kendall  Clough) 133 

*Automatic  Tuning  for  the  Radio  Re- 
ceiver (Leroy  S.  Hubbell) 72 

Aviation  Must  Come  to  the  Use  of  Radio    129 
*Aviation,  What  Radio  Has  Done  for 
(An  English  Radio  Engineer) 288 

*O  SUPPLY,  A  D.  C.  Power  Ampu- 
le fier  and  (Victor  L.  Osgood) 18 

*B  Supply,  A  Space-Charge  Amplifier 

(H.  P.  Manly) 163 

Baird  Television  Apparatus  on  Sale, ...       11 
*Beat-Frequency    Oscillator,    How    to 

Build  a  (G.  F.  Lampkin) 156 

Book  Reviews: 

Bible  Dramas,  by  William  Ford 

Manley  (Carl  Dreher) 304 

Drake's  Radio  Cyclopedia,  by 
Harold     P.     Manly     (Carl 

Dreher) 302 

Elements  of  Radio-Communica- 
tion,  The,  by  O.  F.  Brown 

(Carl  Dreher) 306 

Experimental  Electrical  Engi- 
neering,  by   V.    Karapetoff 

(Carl  Dreher) 280 

Lefax  Radio  Handbook   (Carl 
Dreher) 76 


PAGE 

Popular  Guide  to  Radio,  A,  by 
B.  Francis  Dashiell  (Carl 

Dreher) 76 

Practical  Radio  Telegraphy,  by 

Arthur  R.  Nilson  and  J.  L. 

Hornung  (Carl  Dreher).  ...       56, 

Radio  Engineering  Principles, 

by  Henri  Lauer  and  Harry 

L.  Brown  (Carl  Dreher) 76 

Radio  Theory  and  Operating, 
by  Mary  Texana  Loomis 

(Edgar  H.  Felix) 56 

What  Use  Broadcasting?  by 
William  G.  Shepherd  in 
Mirrors  of  the  Year  (Carl 

Dreher) 274 

Wireless  Direction  Finding  and 
Directional  Reception,  by  R. 

Keen  (Carl  Dreher) 360 

British  Imperial  Radio  System,  Struggles 

of  the 195 

British  Skeptical  of  Baird  Television  Ac- 
complishments   69 

Broadcast  Regulation  at,  a  Standstill ....     130 
Broadcast  Station  Calls  with  a  Past 

(William  Fenwick) 150 

Broadcast  Stations,  Present  Distribution 

of. 69 

*Broadcasting,  How  to  Improve  (John 

Wallace) 31 

*Broadcasting   Is  Accomplished,   How 

Chain  (C.  E.  Dean) 65 

Broadcasting,  More  High  Power 69 

Broadcasting  Needs  Capable  Leadership.       68 
*Building  and  Operating  the  A.  C.  "R. 

B.  Lab."  Receiver  (Hugh  S.  Knowles)      93 
*Building    the    D.    C.    Lab    Receiver 
(Keith  Henney) 199 

/^ALDWELL  Hits  Straight  from  the 

Ls   Shoulder 196 

*Can  We  Multiplex  Our  Radio  Chan- 
nels? (Albert  F.  Murray) 245 

*Chain  Broadcasting  Is  Accomplished, 
How  (C.  E.  Dean) 65 

*Checking  Up  on  Audio  Distortion  (G. 
F.  Lampkin) 290 

*Coast  Survey,  Radio  Helps  in  the 
(D.  L.  Parkhurst) 374 

Commission  Announces  Its  Short-Watie 
Policy,  The 196 

Commission,  Another  Non-Radio  Man 
for  the 131 

Commission  Eliminates  Its  First  Station, 
The 132 

*Compact  and  Inexpensive  "Trouble 
Shooter,"  A  (Emil  Reisman) 273 

Congress  Dabbles  with  tlie  Radio  Situation       10 

*" Cornet"  Multiwave  Receiver,  The 
(W.  H.  Wenstrom) 77 

"Cornet"  Receiver,  Notes  on  the 
(W.H.  Wenstrom)  302 

*Coupling  Methods  for  the  R.  F.  Ampli- 
fier (Bert  Smith) 361 

"Crystal  Receiver  for  the  Beginner,  A 
Good  (Keith  Henney) 97 

*T~y  C.  Lab  Receiver,  Building   the 

\-J    (Keith  Henney) 199 

*D.  C.  Power  Amplifier  and  B  Supply, 

611307 

Bound 


PAGE 

A  (Victor  L.  Osgood) 18 

Direct  Selling  by  Radio  (Francis  St. 
Austell) 58 

Directory  of  Vacuum  Tubes,  "Radio 
Broadcast's" 107,  300 

*Distortion,  Checking  Up  on  Audio  (G. 
F.  Lampkin) 290 

*Dual  Control  A.  C.  Receiver,  A  (Rob- 
ert Burnham) 192 

TfMPTY  Pool,  The 255 

I-*  Engineers   in    Quantity  Production 

of  Standards 255 

Engineers'  Plan  of  Allocation,  The 132 

"Equalization,"  The  Inequalities  of.  .  .  .  131 
*Extra  R.  F.  Stage  for  Any  Receiver,  An 

(The  Laboratory  Staff) 217 

*TTMNE   Program    You    Will   Never 

"    Hear,  A  (John  Wallace) 165 

*5-Meter    Band?    What    About    the 

(Robert  S.  Kruse) 212 

*5-Meter  Hints,   Practical   (Robert  S. 

Kruse) 371 

*5    Meters,    Working   on    (Robert   S. 

Kruse) 263 

*Five-Tube    Screen-Grid    Receiver,    A 

(James  Millen) 20 

*Flexible  A.  C.  Super-Heterodyne,  A 

(Dana  Adams) 39 

*From   Milliammeter   to   Multi-Meter 

(G.  F.  Lampkin) . .  80 

*f~*  OOD  Amplifier-Power  Unit  for  the 
VJ  250  Tube,  A  (Howard  Barclay  .  .     141 
*Good  Crystal  Receiver  for  the  Begin- 
ner, A  (Keith  Henney) 97 

Guggenheim   Fund   Shows   the    Way   to 
'Frisco 253 

TTARRISBURG,  III.  Needs  a  500-watt 

Li    Station 254 

*Haven  of  a  Sea-Going  Audion,  The 

(Raymond  Travers) 116 

Here  and  There 12,  70,  197,  255,  339 

*"Hi-Q  29,"  The— A  Receiver  with  a 
Band-pass  R.  F.  Amplifier  (D.  K. 

Oram) 341 

High-Frequency  Spectrum,  The 

High  Power  Broadcasting,  More 69 

*Home  Study  Sheets,  "Radio  Broad- 
cast's": 

Alternating  Current 357 

Determining  the  Capacity  and 
Inductance  of  a  Radio  Cir- 
cuit   136 

Measuring   the   Amplification 

Factor  of  Tubes 261 

Nature  of  Radio  and  Electric- 
ity, The 135 

Ohm's  Law 206 

Testing  Vacuum  Tubes 205 

Vacuum  Tube  Characteristics.     262 
*How  Can  Good  Radio  Programs  Be 

Created?  (John  Wallace) 104 

*How  Chain  Broadcasting  Is  Accom- 
plished (C.  E.  Dean) 65 

*How  to  Build  a  Beat-Frequency  Os- 
cillator (G.  F.  Lampkin) 156 

How  to  Improve  Broadcasting  (John 
Wallace^ 31 


FE     26   '29 


INDEX— Continued 


PAGE 
INEQUALITIES  of  "Equalization," 

J.    The 131 

"Interesting   A-B-C    Power    Unit    and 
One-Stage  Amplifier,  An  (J.  George 

Uzmann) 145 

*Is  the  Highbrow  Entitled  to  a  Program 
of  His  Own?  (John  Wallace) 223 


EEP    Commercialism    Out    of   the 
Amateur  Bands 254 


K 

*T   ABORATORY  Information  Sheets, 
-L'     "Radio  Broadcast's": 

A.   C.   "Universal"  Receiver, 

The 50 

Amplification  Constant 112 

Audio  Transformer,  The 380 

Calculating  Grid  Bias  for  A.  C. 

Tubes 378 

Circuit  Diagram,  A.  C.  "Uni- 
versal" Receiver 51 

Circuit  of  a   Resistance-Cou- 
pled Screen-Grid  Amplifier.  112 
Circuit  of  the  Roberts  Four- 
Tube  A.  C.  Receiver 298 

Circuits  of  the  Hi-Q  Six,  The.  234 

Current 114 

Dynamic  Loud  Speakers,  The.  380 
Electrical    Measuring    Instru- 
ments   176 

Equalizers 232 

Equalizing     Wire     Lines     for 

Broadcasting 178 

Farm  Lighting  Systems 174 

Filters 382 

Frequency  Characteristic  of  a 

Seven-Mile  Cable 232 

Grid  Bias 50 

Grid  Bias  Circuits  for  A.  C. 

Tubes 378 

Grid  Bias  Measurements 50 

Hi-Q  Six,  The 234 

Impedance-Coupled  Amplifiers  382 

Index,  August  1927-May  1928  51 

Line  Voltage  Variations 176 

Measuring  Instruments ....  234,  296 

"  Motorboating  " 110 

Power  Values  in  Radio  Receiv- 
ing Antennas 178 

Protecting  the  Rectifier  Tube.  230 

Push-Pull  Amplifiers 110 

Radio  Transmission 296 

Resistance-Coupled    Amplifier 

With  Screen-Grid  Tubes,  A  112 

Resistors 114 

Roberts  Four-Tube  A.  C.  Re- 
ceiver, The 298 

Screen-Grid     Resistance-Cou- 
pled Amplifier,  A 178 

Screen-Grid  Tube  as  an  R.  F. 

Amplifier,  The 114 

Selectivity 230 

Servicing  Radio  Receivers.  .  .  .  294 
Size    of    Tap    and    Clearance 

Drills 298 

Soldering  Irons 232 

Telephone  Transmission  Unit, 

The 380 

Text  Books  on  Radio 296 

Tube  Life 174 

Tube  Overloading 48 

Tuned  Circuits 176 

UX-250  and  cx-350.  The 48 

Using    a    Milliammeter   as   a 

Voltmeter 294 

Voltmeter,  The 382 

"Laboratory,  "Strays"  from  the  (Keith 
Henney) : 

A.  C.  Screen-Grid  Tubes 202 

A.  C.  Troubles 83 

Another  Patent  Muddle 260 

Another  Useful  Publication.  .  .  84 
At     Last — A     Line     Voltage 

Regulator 259 

Coil  Dimensions,  An  Error  in .  30 

Detector  Distortion 29 

Engineers  as  Salesmen 347 

"Equamatic"  System  in  Eng- 
land, The 29 

Finding  Ore  by  Radio ?9 


PAGE 

Flux  for  Nichrpme  Wire,  A.  .  .  144 

From  a  Lab  Circuit  Fan 144 

High  Powered  Press  Releases.  83 
Keeping  R.  F.  Current  Out  of 

the  Audio 201 

Line  Voltage  Variations 201 

Loud  Speaker  Tests 202 

Loud  Speakers 30 

Making  D.  C.  Sets  Comfort- 
able   202 

May  Standard  Frequency  Sig- 
nals   84 

More  Radio  Hoaxes 259 

Mortality   Among  the  A.   C. 

Tubes 347 

New  Cyrstal  Control 143 

Output  Transformer  Charac- 
teristics    83 

Present  Compression-Type  Re- 
sistors   144 

Present  Interesting  Trends  in 

Radio 143 

Prices    of    British    "Compo- 
nents"   143 

Publications  Worthy  of  Note  144 

Radio  PS  a  Scapegoat 347 

Radio  School  Scholarships.  .  .  84 

Radio  Gossip 143 

Real  Power  from  Two  112's  .  .  29 
Recent  Articles  of  Interest ...  202 
Recent    Interesting    Contem- 
porary Articles 84 

Recent   Interesting  Technical 

Articles 144 

Remler  A.  F.  Amplifying  Sys- 
tem, The 348 

Screen-Grid    and    Automatic 

Receivers 259 

Screen-Grid  Mystery,  A 347 

Screen-Grid  Tube,  The:  Selec- 
tivity   30 

Short- Wave  Adapter,  A 29 

Short-Wave  Broadcasting.  ...  29 

Short- Wave  Market,  The 201 

Short-Wave  Notes 84 

Short- Wave  Reception 348 

"  Sink  or  Swim  "  Tube  Testing  201 
"Skim  Milk  Masquerades  as 

Cream  " 144 

Some  Coil  Measurements 260 

"Strays"  from  other  Labora- 
tories.   202 

Technical  Smoke  Screen 144 

Tested  Products 29 

Testing  for  Soft  Tubes 348 

Trailing  "Power  Leak"  Inter- 
ference   259 

Two  Interesting  Patents 347 

Who  Our  Readers  Are 144 

Laboratories  Grapple  with  Aircraft  Radio, 

The 253 

Letters  from  Readers 179,  231,  308,  386 

*Lighting  Lines  Safe  for  A.  C.  Tubes, 

Make  Your  (Kasson  Howe) 269 

List  of  Short- Wave  Stations  Throughout 

the  World,  A 44 

'Listeners'  Point  of  View,    The   (John 

Wallace) 31.  104.  165,  223 

Long  Waves  Needed  in  Transoceanic  Serv- 
ice   255 

*Loud   Speakers,    All    About    (Joseph 

Morgan) 188 

Low-Power  Stations  Plead  Their  Case, 

The 337 

X/TACKAY-R.  C.  A.  Struggle,  The.  .  195 
1  VI  *Make  Your  Lighting  Lines  Safe 

for  A.  C.  Tubes  (Kasson  Howe) ....  269 
*Making  an  A-Power  Unit  from  Your 

Battery  Charger  (Robert  Burnham).  137 
Manufacturers'  Booklets 

25,  108,  170,  228,  282,  376 
*Manufactured      Receivers,      "Radio 

Broadcast's  "  Service  Data  Sheets  on 

(See  Service) 91,  159,  221,  277,  369 

"March  of  Radio,  The  (E.  H.  F.) 

9.  68,  129,  195,  253,  337 

Mergers  in  the  Radio  Industry 69 

*Milliammeter  to  Multi-Meter,  From 

(G.  F.  Lampkin) 80 


249 


PAGE 

More  High  Power  Broadcasting 69 

Monopoly  ?  Why  the  Persistent  Cry  of.  .         9 
*Month's   New   Phonograph   Records, 
The 25,  106 

J^TEMA  Convention.  At  the 253 

J.  V  *National  Screen-Grid  Five,  Oper- 
ating the  (James  Millen) 225 

Naval  Stations.  Press,  Weather  and 

Time  Signal  Transmissions  of.  .  52 

*New  Apparatus.  .35,  85,  139,  227.  284,  372 
*New  Principle  in  Audio  Transformer 

Design,  A  (Kendall  Clough) 133 

*New  Transmitting  Methods  be  the 

Remedy?  Will  (Edgar  H.  Felix) 5 

*Newest  Power  Tube,  The  (Howard  E. 

Rhodes) -74 

*Nine-Tube  Screen-Grid  Super,  A 

(Robert  Burnham) 334 

No  Innovations  or  Revolutions  for  1928 . .  130 
*Non-Radiating  Short-Wave  Tuner,  A 

fjames  Millen) 286 

Notes  on  the  "Cornet"  Receiver  (W.  H. 

Wenstrom > 302 

""pvNE-SPOT"  Screen-Grid  Super, 
\J  A  (W.  H.  Hollister) 

""Operating  the  National  Screen-Grid 
Five  (James  Millen) 225 

*Our  Readers  Suggest  .  .  . 

33,  89,  151,  215,  271,  364 

PATENT  Situation,  The 12 
*Phonograph  Records.  The  Month's 
New 25,  106 

*Photo  Broadcasting  in  England  (Wil- 
liam J.  Brittain) 384 

*" Pick-Up"  Shall  I  Buy?  What  (David 
Grimes) 207 

Picture  Broadcasting  Must  Contain  No 
"Ads" 11 

Picture  Transmission,  Regulations  for 
Teletisinn  and 338 

*Power  Attfiplifier  and  B  Supply,  A.  D  C. 
(Victor.  L.  Osgood) 18 

*Power  Supply,  A  Resistance-Coupled 
Amplifier  and  (J.  George  Uzmann).  .  257 

*Power  Tube,  The  Newest  (Howard  E. 
Rhodes) 74 

*Practical  5-Meter  Hints  (Robert  S. 
Kruse) 371 

Present  Distribution  of  Broadcast  Sta- 
tions   69 

Press,  Weather  and  Time  Signal  Trans- 
missions of  Naval  Stations 52 

*"O  B.  LAB."  Receiver,  Building 
iv.  and  Operating  the  (Hugh  S. 
Knowles) 93 

*"R.  B.  Lab."  Receiver,  A  Short-Wave 
Adapter  for  the  (Hugh  S.  Knowles) . .  153 

"Radio  Broadcast's"  Directory  of  Vac- 
uum Tubes 107,  300 

*" Radio  Broadcast's"  Home  Study 
Sheets  (See  Home) 135,  205,  261,  357 

""Radio  Broadcast's"  Laboratory  In- 
formation Sheets  (See  Laboratory) 

48,  110,  174,  230,  294,  378 

*" Radio  Broadcast's"  Service  Data 
Sheets  on  Manufactured  Receivers 
(See  Service) 91,  159,  221,  277,  369 

*Radio  Channels?  Can  We  Multiplex 
Our  (Albert  F.  Murray) 245 

*R.  F.  Amplifier,  Coupling  Methods  for 
the  (Bert  E.  Smith). 361 

*R.  F.  Amplifier,  The  222  Tube  as  an 
(Glenn  H.  Browning) 252,  359 

*R.  F.  Stage  for  Any  Receiver,  An  Extra 
(The  Laboratory  Staff) 217 

*Radio  Helps  in  the  Coast  Survey  (D. 
L.  Parkhurst). 374 

Radio  Laughs  at  Wired  Wireless 10 

*Receiver  for  Short-Wave  Broadcast 
Reception  (Bert  E.  Smith) 167 

Recent  Radio  Events 132 

Regulations  for  Television  and  Picture 
Transmission 338 

"Resistance-Coupled  Amplifier  and 
Power  Supply,  A  (J.  George  Uzmann)  257 

*Right  Audio  Combination,  The  (L.  W. 
Hatry) 23 


INDEX— Continued 


91 
369 
221 

222 
159 
160 

278 
92 

370 


PAGE 

*Roberts  Receiver,  A  Three-Tube  A.  C. 
Operated  (Elmer  G.  Hery) 99 

*QARGENT-RAYMENT  Seven  Re- 
O  ceiver.  The  (Howard  Barclay) . . .     354 
*Screen-Grid  Booster  for  Any  Receiver, 

A  (Glenn  H.  Browning) 87 

*Screen-Grid    Receiver,    A    Five-Tube 

(James  Millen) 20 

*Screen-Grid  Receiver,  An  A.  C 37 

*Screen-Grid  Short-Wave  Receiver,  A 

(Howard  Barclay) 203 

*Screen-Grid  Tube  in  Popular  Circuits, 

Using  the  (Laboratory  Staff) 96 

*Screen-Grid     Tuner,     A     Two-Tube 

(Glenn  H.  Browning) 27 

*S8reen-Grid  Tuner,  A  Two-Tube  A.  C. 

(James  Millen) 349 

*Service  Data  Sheets  on  Manufactured 
Receivers,  "Radio  Broadcast's": 

Amrad,  A.  C.  7,  The 

Bosch  Model  28  Receiver,  The 

Fada  480-B,  The 

Federal     Ortho-sonic     Seven- 
Tube  Receiver,  The 

Grebe  A.  C.  Six,  The 

Kolster  6K  A.  C.,  The 

Marconiphone  Model  61  Re- 
ceiver, The 

Pfansteihl  A.  C.  34  and  50.  The 
Splitdorf    "Inherently    Elec- 
tric "  Receiver,  The 

Stromberg-Carlson    Receivers 

Nos.  635  and  636 277 

"Short- Wave  Adapter  for  the  R.  B.  Lab. 

Receiver,  A  (Hugh  S.  Knowles).  .  . .     153 
*Short-Wave  Broadcast  Reception,   A 

Receiver  for  (Bert  Smith) 167 

*Short-Wave  Code  Signals,  A  Super- 
Heterodyne  for  (Lloyd  T.  Goldsmith) 
Short- Wave  Policy,  The  Commission  An- 
nounces Its 

*Short-Wave    Receiver,    A    Universal 

(Lloyd  T.  Goldsmith) I... 

Short-Wave  Stations  Throughout  ffte 

World,  A  List  of 

*Short-Wave  Transmitter  for  1929,  A 

(Robert  S.  Kruse) 344 

*Short-Wave  Tuner,  A  Non-Radiating 

(James  Millen) 

*Simple  Unit  for  Measuring  Impedances 

A  (F.  J.  Fox  and  R.  F.  Shea) 

*Six-Tube  Screen-Grid  Receiver,  A  (Mc- 

Murdo  Silver) 

*Space-Charge  Amplifier  and  B  Supply, 

A  (H.  P.  Manly) 163 

""Strays"  from  the  Laboratory  (Keith 
Henney)  (See  Laboratory) 

29,  83,  143,  201,  261 
Struggles  of  the  British  Imperial  System . 
*Super,     A     Nine-Tube,     Screen-Grid 

(Robert  Burnham) 

*Super-Heterodyne,  A  Flexible  (Dana 

Adams) 

""Super-Heterodyne     for     Short-Wave 
Code  Signals,  A  (Lloyd  T.  Goldsmith) 


15 

196 

13 

44 


286 
279 
281 


347 
195 

334 
39 
13 


'TELEVISION: 
A          Baird  Television  Apparatus  on 

Sale 11 

Television  and  Picture  Trans- 
mission, Regulations  for 338 

*Television — Its  Progress  To- 
day (Howard  E.  Rhodes).. .     331 


PAGE 

*What  Can  We  See  By  Radio? 

(R.  P.  Clarkson) 185 

*What  Hope  for  Real  Televi- 
sion? (R.  P.  Clarkson) 125 

Ten-Meter  Band.  Amateurs  in  the 197 

Tester,  A  Universal  Set  and  Tube  (D. 

A.  R.  Messenger) 148 

Three-Tube  A.  C.  Operated  Roberts 

Receiver.  A  (Elmer  G.  Hery) 99 

Transmitting  Methods  be  the  Remedy? 

Will  New  (Edgar  H.  Felix) 5 

Transoceanic  Service,  Long  Waves  Needed 

in 255 

"Trouble  Shooter,"  A  Compact  and 

Inexpensive  (Emil  Reisman) 273 

Tuning  for  the  Radio  Receiver,  Auto- 
matic (Leroy  S.  Hubbell) 72 

Two-Tube  A.  C.  Screen-Grid  Tuner,  A 

(James  Millen) 349 

Two-Tube     Screen-Grid     Tuner,     A 

(Glenn  H.  Browning) 27 

*222  Tube  as  an  R.  F.  Amplifier,  The 

(Glenn  H.  Browning). 252,  359 

*T  TNIVERSAL  Set  and  Tube  Tester, 
U  A  (D.  A.  R.  Messenger) 148 

*Universal  Short-Wave  Receiver,  A 
(Lloyd  T.  Goldsmith) 13 

*Using  the  Screen-Grid  Tube  in  Popular 
Circuits  (Laboratory  Staff) 96 

VACUUM    Tubes,    "Radio    Broad- 
cast's" Directory  of 107,  300 

""Vivetone  29"  Receiver,  The  (R.  F. 
Goodwin) 366 

TT/'AR  on  the  Short  Waves,  The .  .  195 

FT  *What  About  the  5-Meter  Band? 

(R.  S.  Kruse) 212 

*What  Can  We  See  by  Radio?  (R.  P. 

Clarkson) 185 

*What  Hope  for  Real  Television?  (R.  P. 

Clarkson) 125 

*What  "Pick-Up"  Shall  I  Buy?  (David 

Grimes) 207 

Why  the  Persistent  Cry  of  Monopoly  ? .  .  9 
*Will  New  Transmitting  Methods  Be 

the  Remedy?  (Edgar  H.  Felix) 5 

*Working  on  5  Meters  (Robert  S.  Kruse)  263 


AUTHORS 


Adams,  Dana. 


39 


Barclay,  Howard 141,  203,  354 

Brittain,  William  J 384 

Browning,  Glenn  H 27,  87,  252,  359 

Burnham,  Robert 137,  192,  334 

Clarkson,  R.  P.  .                              . .  125,  185 
Clough,  Kendall 133 


Dean,  C.  E.  . 
Dreher,  Carl. 


65 


.  .  .42,  56,  76,  102,  161,  219, 
267,  274,  280,  302,  352,  360 
Felix,  Edgar  H. 

5,  9,  56,  68,  129,  195,  253,  337 

Fenwick,  William 150 

Fox,  F.  J 279 

Goldsmith,  Lloyd  T . .  13,  15 

Goodwin,  R.  F 366 

Grimes,  David 207 

Grove,  Herbert.  .  210 


PAGE 

Hatry,  L.  W.  . . .  23 

Henney,  Keith 29,  97,  143,  199,  259,  347 

Hery,  Elmer  G 99 

Hollister.  W.  H 249 

Howe,  Kasson ....     269 

Hubbell,  Leroy  S 72 

Knowles,  Hugh  S. .  .  .93,  153 

Kruse,  Robert  S 212,  267,  344,  371 

Lampkin,  G.  F 80,  156,  290 

Manly,  H.  P..  .  163 

Messenger,  D.  A.  R 148 

Millen.  James 20,  225,  286,  349 

Morgan,  Joseph 188 

Murray,  Albert  F 245 

Oram,  D.  K 341 

Osgood,  Victor  L 18 

Parkhurst,  D.  L 374 

Reisman,  Emil 273 

Rhodes,  Howard  E 74,  331 

St.  Austell,  Francis 58 

Shea,  R.  F 279 

Silver,  McMurdo 281 

Smith,  Bert 167,  361 

Travers.  Raymond 116 

Uzmann,  J.  George 145,  257 

Wallace,  John ..                           ..31,104,223 
Wenstrom,  W.  H 77,  275,  302 

PORTRAITS 
(*Portraits  in  "The  March  of  Radio") 

*Butman,  Carl  H 69 

*Caldwell,  O.  H.  .  69 

Conrad,  Frank 331 


*Duffy,  J.  P 

Evans,  Leroy .... 


Klemm,  Gustav. 
*Korn 


9 
105 


..     166 
11 


*Lafount,  H.  A 69 

Marconi,  G 337 

Nakken,  Theodor 185 

*Pickard,  Sam 69 

Ray.  Bill 166 

*Robinson,  I.  E 69 

Stern,  Samuel  Maurice 105 

*Sykes,  E.  0 69 

Weiner,  Michael 105,  223 

Zahm,  Edna 165 


Copyright,  1928,  by 
DOUBLEDAY,  DORAN  &  COMPANY,  INC. 


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Name Age.. 

Address 


RADIO    BHOADCAST.      May.     1928. 


Published    monthly.       Vol.     XIII,     No 
Garden  City.  N.    Y.,    as   second  <• 


1.        Published 

iss   mail    matter. 


c.inlci]    City.    N.     Y.       Stiln.cn (Minn    price    $  1.00    a    year. 
p.mbh'day.    I>.iran  &   Compunj .    In..,    Canieii   city,    X.    Y. 


Entered    at    the    post   office    at 


RADIO  BROADCAST 


MAY,  1928 


WILLIS  KINGSLEY  WING,  Editor 

KEITH  HENNEY  EDGAR  H.  FELIX 

Director  of  the  Laboratory  Contributing  Editor 


Vol.  XIII.  No.  1 

»• 


Cover  Design  -  -  -  From  a  Design  by  Harvey  Hopkins  Dunn 
Frontispiece  -  Radio  Service  in  a.  Philadelphia  Hotel 
Will  New  Transmitting  Methods  Be  the  Remedy?  Edgar  H.  Felix 
The  March  of  Radio  An  Editorial  Interpretation 


Why  the  Persistent  Cry  of  Monopoly? 
Radio  Laughs  at  Wired  Wireless 
Congress  Dabbles  With  the  Radio  Situation 
Baird  Television  Apparatus  on  Sale 


Picture  Broadcasting  Must  Contain  No  "Ads" 
Annual  Report  of  the  R.  C.  A. 
Here  and  There 
The  Patent  Situation 


A  Universal  Short- Wave  Receiver  -        Lloyd  T.  Goldsmith 

A  Super-Heterodyne  for  Short- Wave  Code  Signals 

Lloyd  T.  Goldsmith 
A  D.C.  Power  Amplifier  and  B  Supply  -  Victor  L.  Osgood 

A  Five-Tube  Screen-Grid  Receiver James  Millen 

The  Right  Audio  Combination      -    -    -  -    L.  W.  Hatry 

The  Month's  New  Phonograph  Records 

A  Two-tube  Screen-Grid  Tuner    •••_••   Glenn  H.  Browning 
"Strays"  from  the  Laboratory        Keith  Henney 

Detector  Distortion 

A  Short-Wave  Adapter 

Short-Wave  Broadcasting 

The  "Equamatic"  System  in  England 

Finding  Ore  by  Radio 

Real  Power  from  two  ill's 

How  to  Improve  Broadcasting 

The  Listeners'  Point  of  View 

Our  Readers  Suggest  -    -    - 

Remote  Volume  Control 
Improving  Your  B  Device 
Plate  Detection 

New  Apparatus 

An  A.C.  Screen-Grid  Receiver 
A  Flexible  A.C.  Super-heterodyne 
As  the  Broadcaster  Sees  It    -    -    - 


Tested  Products 

The  Screen-Grid  Tube:  Selectivity 

Loud  Speakers 

An  Error  in  Coil  Dimensions 

The  A.  C.  "Lab"  Receiver 


John  Wallace 


Adjusting  Cone  Loud  Speakers 
Selectivity  With  A.  C.  Tuhes 


Dana,  Adams 


Design  and  Operation  of  Broadcasting  Stations: 
jy.  Frequency  Runs 


Radio  Folk  You  Should  Know:  Ho.  5  E.  B. 
PMibury 


A  List  of  Short- Wave  Stations  Throughout  the  World 
"Radio  Broadcast's"  Laboratory  Information  Sheets 


No.  185  Tube  Overloading 

No.  186  The  UX-i?o  an 

No.  187  Grid  Bias 

No.  188  Grid  Bias  Measurements 

No.  189  The  A.  C.  "Universal"  Receiver 


No.  IQO  Circuit  Diagram,  A.  C.  "Universal" 

Receiver 

No.   IQI  Index,  August  1017 — May  1918 
No.  191  Index,  August  1927 — May  1918 


Press,  Weather  and  Time  Signal  Transmissions  of  Naval  Stations 

Manufacturers'  Booklets  Available 

Book  Reviews 


(i).  Radio  Theory  and  Operating,  Loomis 

(2).  Practical  Radio  Telegraphy,  Nilson  and  Hornung 


Direct  Selling  by  Radio 


4 
5 
9 


15 
18 

20 
23 
25 
27 
29 


3i 

33 


35 
37 
39 
42 

44 
48 


52 
54 
56 


Francis  St.  Austell     58 


The  contents  of  this  magazine  is  indexed  in  The  Readers'  Guide 
to  Periodical  Literature,  which  is  on  file  at  all  public  libraries. 


TO  OUR  READERS 

BECAUSE  we  value  very  highly  the  confidence  of  our 
readers,  we  present  here  a  few  words  about  the  editorial 
policy  of  this  magazine  as  it  affects  the  problem  of  editorial 
ethics.  The  readers  of  RADIO  BROADCAST  are  much  like  the 
readers  of  a  magazine  devoted  to  book  reviews.  In  the  latter, 
editorial  articles  must  deal,  perforce,  with  the  same  subjects  as 
found  in  the  advertising  pages.  In  RADIO  BROADCAST  our 
text  pages  must  very  often  contain  articles  describing  the 
use  of  units  featured  in  the  advertising  pages.  But  how  long 
would  you  read  a  book  review  publication  if  all  reference  to 
publisher,  price  and  author  were  omitted?  And  how  long  would 
you  read  such  a  magazine  if  you  felt  there  were  collusion  be- 
tween editorial  and  advertising  content? 

ALL  of  the  articles  in  this  magazine — constructional  ones, 
especially — are  chosen  for  one  reason,  only,  because  we 
think  they  are  interesting  and  useful  to  our  readers.  We  are 
frank  about  mentioning  parts  employed  because  we  believe  our 
readers  want  to  know  that  information.  We  have  in  the  past 
and  will  continue  to  indicate  in  the  future  the  possibilities  of 
substitution  of  parts,  leaving  the  actual  construction  to  the 
judgment  of  the  reader.  The  reader  has  a  right  to  know  just 
how  any  circuit  we  describe  was  built,  what  it  costs,  and 
whose  parts  are  used.  In  RADIO  BROADCAST,  all  this  essential 
information  is  in  the  article.  You  will  not  have  to  write  us  for 
additional  circuit  diagrams,  a-  list  of  parts  or  other  essential 
information  which  should  be  in  the  article  in  the  first  place. 
Our  duty  to  the  reader  is  to  give  him  articles  which  are  inter- 
esting, useful,  and  complete.  If  he  encounter  difficulties,  our  Tech- 
nical Information  Service  will  help  him  by  mail,  and  the  editor 
will  always  be  pleased  to  hear  of  the  results  he  achieves. 

THE  technical  accuracy  of  every  statement  made  in  this 
magazine  is  carefully  checked  by  Radio  Broadcast  Labora- 
tory, manned  by  radio  engineers  all  of  whom  have  technical 
university  training.  Their  vigilance  fortifies  every  article.  Arti- 
cles from  the  staff  present  material  not  available  elsewhere,  some 
of  it  constructional,  some  more  general,  but  all  with  the  definite 
purpose  to  be  as  sound  and  accurate  as  we  know  how.  These 
requirements  invariably  apply  to  all  our  articles,  whatever  their 
source.  Our  Laboratory  will  continue  to  originate  useful  cir- 
cuits of  all  sorts;  contributions  from  independent  radio  workers 
are  constantly  sought  and  will  regularly  appear.  Articles,  con- 
structional or  otherwise,  originating  in  manufacturers'  labora- 
tories will  be  published  with  their  origin  made  quite  clear,  only 
when  the  articles  meet  our  rigid  requirements.  This  is  and  has 
been  our  practical  conception  of  responsibility  to  the  reader. 

THE  news  of  radio  developments,  no  matter  where  they 
originate,  is  important,  so,  naturally,  the  activities  of  radio 
manufacturers  will  be  reported  in  these  pages,  but  no  such 
articles  have  appeared  or  will  appear  merely  because  of  their 
advertising  potentialities.  The  reader  need  not  fear  that  this 
magazine  will  overflow  with  articles  thinly  masking  manufac- 
turers' publicity.  Is  it  good?  Is  it  useful?  Is  it  important? — 
those  questions  must  be  satisfactorily  answered  before  the 
article  appears  in  our  pages,  whether  or  not  the  article  originates 
with  a  manufacturer.  It  is  only  natural  if  readers  respect  our 
text  pages  that  the  advertiser  should  find  our  advertising  pages 
valuable,  and  it  is  obvious  that  no  publication  can  long  exist 
without  high  standards  in  both  editorial  and  advertising  con- 
tent. — WILLIS  KINGSLEY  WING. 


DOUBLEDAT,  DORAN  &  COMPACT,  I^C.,  Garden  Qity,  J^ew 


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Copyright,  1928,  m  the  United  States,  Newfoundland,  Great  Britain,  Canada,  and  other  countries  by  Doubleday,  Dor  an  C"  Company,  Inc.     All  right!  reserved. 

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Radio  Service  in  a  Philadelphia  Hotel 


r|^HE  Hotel  Robert  Morris  in  Philadelphia,  in  common  with 
A  many  other  hotels  in  the  United  States,  has  provided  its 
guests  with  a  compelling  reason  to  stay  in  their  rooms  in  the 
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Networks  of  the  National  Broadcasting  Company  or  the  Colum- 
bia chain.  The  radio  control  room  is  located  on  the  top  floor  of  the 
hotel  and  the  equipment,  in  the  main  office  on  the  first  floor,  is 
operated  by  remote  control.  Constant  volume  level  throughout 
the  hotel  is  maintained  by  using  compensating  and  repeating 
coils.  By  grouping  the  jacks  in  the  various  rooms  in  parallel  series 
it  is  possible  to  maintain  reception  in  every  room  in  the  hotel 
even  though  trouble  develop  in  the  outlet  in  one  or  more  rooms. 


WHIPPANY 


the  Remedy^ 


By  Edgar  H.  Felix 


THE    acuteness  of  the   broadcasting  con- 
gestion problem  focusses  public  attention 
upon  any  method  suggested  to  increase  the 
capacity  of  the  broadcasting  band.  Many  pro- 
posals  have   been   made,   some  of  which   hold 
promise  and  others  which,  if  put  into  practice, 
would  only  increase  the  existing  con- 
fusion. Since  the  regulation  of  broad-         __ 
casting  has  become  a  political  matter,       "^* — 
the  great  danger  exists  that  the  state- 
ments   of   pseudo-scientists    may   be 
accepted  and  untried  plans  for  station 
synchronization    will   be  forced   into 
practice  before  they  have  been  fully 
developed. 

There  are  only  two  possible  ways  of 
reducing  congestion  in  the  broadcast 
band:  (i),  large  numbers  of  stations 
must  be  eliminated,  reduced  to  part 
time,  or  curtailed  in  power,  or  (2),  the 
number  of  stations  of  a  given  power, 
successfully  occupying  the  same  chan- 
nel, must  be  increased.  Time  division 
is  already  practiced  to  such  an  extent 
that  further  relief  cannot  be  expected 
from  this  source  without  too  much 
restriction  of  the  service  and  earning 
power  of  existing  stations.  Power  re- 
duction will  only  lessen  the  value  of 
better  stations;  the  tendency  is  toward 
increased  power  because  it  means 
better  program  service  for  greater 
numbers.  Legal  and  political  con- 
siderations make  it  impossible  to  ex- 


pect  wholesale  station  elimination  as  a  source  of 
the  radical  improvement  necessary  for  good 
broadcasting  service  in  every  section  of  the 
country. 

Consequently,    the    only    measure    of    relief 
which  can  be  effective  is  the  development  of 


-n* 


Service  Range  and  Interference  Range 

'"THE  following  table  shows  how  the  power  radiated  by  a  broadcasting  station 
A  affects,  (a)  the  "service  range,"  which  is  that  distance  over  which  good  recep- 
tion will  be  possible  independent  of  static,  day  and  night,  rain  or  shine;  and  (b) 
the  "interference  range,"  which  is  that  distance  over  which  the  carrier  wave  of 
a  broadcasting  station  can  mar  reception  by  generating  a  heterodyne  whistle 
with  the  carrier  wave  of  another  station: 

MILES 


ANTENNA 

SATISFACTORY 

HIGH-GRADE 

CARRIER 

POWER  IN  WATTS 

SERVICE 

SERVICE 

INTERFERENCE 

RANGE 

5 

10 

1 

100 

50 

22.5 

3 

250 

500 

65 

10 

625     . 

5000 

160 

30 

1500 

50,000 

350 

90 

3000 

If  we  divide  the  interference  range  by  the  high-grade  service  range  we  get  the 
following  figures: 


ANTENNA 
POWER  IN  WATTS 
5 
50 
500 
5000 
50,000 


INTERFERENCE   RANGE   DIVIDED 
HIGH-GRADE  SERVICE  RANGE 
100 
83 
62.5 
50 
33 


The  figures  in  the  right-hand  column  show  clearly  that  high-power  stations 
approach  closer  to  the  ideal  condition  as  the  ratio  of  the  interference  range  to  the 
service  range  is  decreased. 


some  means  of  increasing  the  number  of  stations 
of  present  powers  operating  on  the  same  channel 
without  interference.  Many  schemes  to  effect 
this  result  have  been  offered.  They  fall  into  three 
classifications: 

(i)  The  elimination  of  the  carrier  whistle  by 
accurate  control  of  the  carrier  fre- 
quency of  stations  occupying  the 
same  channel,  permitting  service 
range  rather  than  carrier  range  to 
determine  the  necessary  spacing 
between  stations  on  the  same 
channel; 

(2)  The  synchronization  of  both  car- 
rier and  program,  popularly  refer- 
red to  as  placing  chain  stations  on 
a  single  channel; 

(3)  The  limitation  of  the  carrier  range 
to  the  service  range  of  the  station 
by  the  application  of  new  princi- 
ples of  transmission. 

Before  considering  in  detail  the 
actual  methods  for  each  of  these 
general  systems,  what  are  the  require- 
ments for  a  plan  which  will  increase 
the  capacity  of  the  broadcasting  band? 
Four  major  qualifications  must  be  met 
and  failure  to  meet  any  one  of  them 
condemns  any  suggestion  as  useless. 
They  are: 

(i)  The  system  must  be  of  unfailing 
reliability  in  operation.  The  adop- 
tion of  closer  spacing  among  sta- 
tions on  the  same  channel,  the 
objective  of  most  of  the  systems. 


RADIO  BROADCAST 


MAY,  1928 


\ 
\ 
\ 


means  that  their  temporary  or  per- 
manent failure  will  bring  heterodyne 
whistles  of  much  greater  intensity  than 
are  experienced  under  present  conditions. 

(2)  The  system  must  not  demand  an  order  of 
operating  skill  beyond  that  obtainable  by 
average  broadcasting  station  staffs. 

(3)  The  first  cost  of  equipment  required  and 
its  maintenance  expense  must  not  be  so 
high  as  to  place  it  beyond  the  financial 
capacity   of   average    broadcasting   sta- 
tions. 

(4)  The  adoption  of  the  system  must  not 
require    any    substantial    alteration    in 
transmitting   and    receiving    equipment 
and  must  entail  no  sacrifice  in  quality  of 
reproduction. 


We  will  examine  each  proposal  in  the  light  of 
these  four  qualifications.  The  first 
general  class  of  methods  concerns 
those  intended  to  eliminate  the  car- 
rier heterodyne  or  whistling  inter- 
ference with  which  all  listeners  are 
now  painfully  familiar.  The  pitch  of 
the  carrier  whistle  depends  upon  the  , 

difference  in  frequency  between  the 
twoor  more  carriers  simultaneously 
actuating  the  receiving  set.  Suppose 
we  have  two  stations  assigned  to  a 
million  cycles,  or  300  meters,  one 
precisely  on  the  assigned  frequency; 
the  other  one  half  of  one  per  cent, 
above  it,  or  on  1,005,000  cycles.  The 
resultant  effect  will  be  to  impose  a 
5Ooo-cycle  note  upon  the  programs 
of  both  stations.  If  one  station 
deviates  a  hundredth  of  i  per  cent, 
from  the  assigned  frequency,  the 
resultant  heterodyne  will  be  a  hun- 
dred cycles.  Accuracy  of  one  part  in 
a  hundred  thousand  is  therefore 
essential  if  the  carrier  heterodyne  is 
to  be  reduced  to  a  point  below  audi- 
bility. In  that  case,  the  maximum 
heterodyne  note  would  be  20  cycles, 
assuming  that  both  stations  have 
deviated  in  opposite  directions  from 
the  assigned  frequency.  Note  the  ex- 
traordinary stability  necessary  to 
permit  two  carriers  to  overlap  with- 
out heterodyne. 

The  intensity  of  the  whistle  heard 
at  a  receiving  point  is  dependent 
upon  the  carrier  energy  received 
from  the  more  distant  station.  The 
degree  to  which  it  mars  reception 
depends  somewhat  upon  the  ratio 
of  the  carrier  whistle  to  the  amount 
of  modulation  received  from  the 
nearer  station.  An  understanding  of 
these  two  statements  will  reveal  why 
carrier  synchronization  will  effec 
real  relief  under  present  conditions. 
You  have  frequently  heard  a  hetero- 
dyne of  considerable  intensity  and  waited  for  the 
local  station  to  sign  off,  in  the  hope  that  you 
could  identify  the  distant  station  causing  the 
whistle.  But  you  find  it  impossible  to  hear  the 
slightest  sound  from  the  distant  station.  This  is 
due  to  the  fact  that  the  carrier  spreads  from  thirty 
to  forty  times  the  distance  that  a  high-grade  pro- 
gram signal  is  heard  and  also,  because  of  the 
square  law  operation  of  the  detector  tube,  the 
carrier  is  subject  to  much  greater  amplification 
than  the  audio-frequency  modulation  impressed 
on  it 


maximum  high-grade  service  range  of  a  joo-watt 
station  is  30  miles,  but  its  average  carrier  range 
is  at  least  1000  miles  and  often  over  2000  miles. 
Under  average  conditions,  it  delivers  a  dis- 
tinguishable program  signal  to  sensitive  receivers 
for  perhaps  350  or  400  miles.  If  two  stations  on 
the  same  channel  are  perfectly  synchronized, 
they  would  have  to  be  spaced  only  400  to  500 
miles  apart,  without  suffering  audio-frequency 
distortion  within  their  respective  local  service 
ranges.  But,  under  present  conditions,  ijoo-mile 
separation  is  necessary  to  reduce  carrier  hetero- 
dyne to  the  point  that  local  reception  is  not 
noticeably  affected  and  complaints  are  often 
registered  with  respect  to  heterodynes  caused  by 
50o-watt  stations  2000  miles  distant  from  the 
receiving  point. 


Circle  No  1  HIgrKJride  Service  Range 
Circle  No.  2  Satisfactory  Service  Rtnge 
Circle  No.  3  Interference  Range 


\ 

\ 

i, 

i- 


\ 


\ 


\ 


SERVICE  AREA  AND  INTERFERENCE  RANGE 
The  circles  show  the  relative  areas  of  high-grade  service  range,  satis- 
factory service  range,  and  interference  range,  of  a  jo.ooo-watt  broad- 
casting station.  Note  how  large  the  interference  range  is  in  comparison 
to  the  service  range.  The  actual  service  area  of  this  station  does  not 
extend  beyond  the  area  enclosed  by  circle  No.  2,  for  at  greater  distances, 
static  and  fading  will  interfere  with  good  reception.  The  much  larger 
area  of  circle  No.  3  extends  far  beyond  the  area  of  fair  reception. 
Within  this  large  area  the  station  can  create  interference  by  generat- 
ing a  heterodyne  with  the  carrier  wave  of  another  station,  supposedly 
operating  on  the  same  frequency,  but  actually  transmitting  on  a  fre- 
quency slightly  higher  or  lower.  Accurate  stabilization  of  the  carrier 
frequencies  of  stations  operating  on  similar  frequencies — perhaps  by 
the  quartz  crystal  method — will  prevent  heterodyne  interference  but 
will  not  prevent  interference  arising  from  the  clashing  of  sidebands 


Four  methods  have  been  suggested  for  stabiliz- 
ing the  carriers  of  broadcasting  stations  so  as  to 
eliminate  the  possibility  of  carrier  whistle: 

(1)  Stable  precision  crystal  oscillators; 

(2)  Remote   manual   control  of  carrier  fre- 
quency; 

(3)  Radio   transmission   of  a  reference  fre- 
quency; and 

(4)  Wire  synchronization  of  carriers. 


WHY   STATIONS   ARE    SPACED 

IN  PRACTICE,  this  condition  accounts  for  the 
great   spacing   required    between  stations  of 
moderate  power,  if  the  service  area  of  each  of 
them   is  to  enjoy   undisturbed   reception.   The 


The  zero-beat  method,  employing  crystal 
control  oscillators,  is  now  widely  used.  The  sta- 
tion operator  wears  a  headphone  through  which 
courses  the  output  of  the  crystal  oscillator  and 
also  the  station's  radiated  carrier  frequency. 
The  frequency  of  the  station  is  adjusted  until 
the  two  are  in  exact  synchronism  so  that  no 
heterodyne  whistle  is  heard. 


In  preparing  to  write  this  article,  the  author 
maintained  a  broadcasting  station  on  its  fre- 
quency by  the  zero-beat  method  for  several 
programs.  When  utilizing  a  crystal  oscillator, 
installed  at  the  station,  the  comparison  signal 
is  constant  and  powerful.  The  amount  of  skill 
required  and  the  cost  of  maintenance  of  the 
equipment  needed  are  within  the  reach  of  any 
broadcasting  station. 

Independent    crystal    control,    however,    has 

been  described  as  too  inaccurate  and  too  unstable 

to  permit   the  perfect  synchronization  of  two 

carriers.  As  a  matter  of  fact,  there  is  no  inherent 

fault  in  the  crystal  oscillator  which  cannot  be 

corrected.  What  are  needed  are  perfected  means 

of  supplying  crystal  oscillators  with  absolutely 

constant  voltages  and  means  of  maintaining  the 

crystal    at   an   absolutely   constant 

temperature. 

A  change  of  one  degree  centigrade 
varies  the  frequency  of  a  crystal  os- 
cillator by  sixty  to  a  hundred  cycles. 
The  crystal  oscillator  is  usually  in- 
stalled in  a  penthouse  on  the  roof  of 
a  building  where  the  transmitter  is 
installed.  Heat  supply  is  often  un- 
certain in  such  exposed  locations  and 
temperature  variations  of  twenty 
degrees,  during  operating  hours,  are 
not  uncommon.  Such  a  change  is 
sufficient  to  cause  a  2Ooo-cycle  vari- 
ation in  the  frequency  of  a  crystal 
oscillator. 

Crystals  have  been  submitted  to 
laboratories  by  broadcasting  station 
owners  with  a  view  to  finding  out 
why  they  do  not  hold  the  station  to 
its  assigned  frequency.  Among  these 
are  ordinary  quartz  lenses,  crudely 
scratched  and  insecurely  mounted  in 
contacting  clamps.  These  worse- 
than-useless  crystals  have  been  sold 
to  broadcasting  stations  with  the 
expectation  that  they  will  stabilize 
carrier  frequencies.  The  fact  that  a 
station  uses  crystal  control  is  no 
guarantee  whatever  that  it  will  re- 
main accurately  on  its  frequency 
any  more  than  providing  an  aviator 
with  a  compass  assures  that  he  will 
arrive  safely  at  a  distant  destination. 
Proponents  of  the  crystal  oscilla- 
tor method  have  sometimes  proved 
their  case  by  setting  up  two  such 
oscillators  in  the  laboratory,  both 
using  a  slab  from  the  same  quartz 
crystal.  Such  demonstrations,  how- 
ever, prove  nothing  because  both 
oscillators  are  then  working  under 
exactly  the  same  conditions.  When 
one  of  the  oscillators  is  shipped  to  a 
distant  station  to  control  its  carrier, 
varying  temperature  conditions 
cause  sufficient  deviation  to  produce  annoying 
heterodynes.  With  equipment  now  commercially 
available,  the  crystal  oscillator  does  not  possess 
sufficient  stability  to  eliminate  the  heterodyne 
whistle  between  two  stations  operating  on  the 
same  channel.  Nevertheless,  development  of 
precision  oscillators,  with  accurate  temperature 
control,  is  a  most  promising  line  of  research. 

MANUAL    CONTROL    OF    FREQUENCY 

A  NUMBER  of  enthusiasts  have  loudly 
heralded  their  success  in  synchronizing 
their  station's  carrier  with  a  single  interfering 
station  by  checking  the  heterodyne  with  a  receiv- 
ing set  remote  from  the  broadcasting  station. 
This  is  the  second  method  listed.  By  means  of  a 
wire  connection  with  the  station,  the  carrier 
frequency  is  varied  until  the  observed  heterodyne 


MAY,  i9a8 


WILL  NEW  TRANSMITTING  METHODS  BE  THE  REMEDY? 


disappears.  Because,  in  isolated  instances,  two 
stations  have  employed  this  method  successfully, 
it  has  been  hailed  as  a  panacea.  In  those  cases 
where  two  stations,  assigned  to  the  same  channel, 
cause  a  heterodyne  sufficiently  loud  to  permit 
of  easy  elimination  by  the  zero-beat  method, 
they  both  suffer  audio-frequency  distortion,  due 
to  the  interaction  of  their  programs,  even 
within  their  immediate  service  areas. 

Although  the  heterodyne  whistle  may  be 
eliminated,  the  system  does  not  permit  of  ac- 
curate synchronization  unless  the  receivers  used 
respond  to  frequencies  below  sixty  cycles.  Fur- 
thermore, the  scheme  merely  accomplishes  ap- 
proximate synchronization  between  two  stations 
and  affords  no  assurance  that  either  station  is  on 
its  assigned  frequency.  Should  any  number  of 
stations  on  the  same  channel  use  this  plan,  that 
frequency  would  become  a  raving  bedlam,  each 
station  trying  to  follow  the  others,  each  not 
knowing  what  changes  to  expect  in  the  frequency 
of  the  others.  The  difficulties  of  manual  fre- 
quen<-y  control  can  best  be  appreciated  by  set- 
ting up  three  or  four  regenerative  receivers  in 
neighboring  houses,  adjusting  them  all  in  an 
oscillating  condition  upon  a  predetermined 
broadcasting  station,  and  maintaining  them 
there  without  permitting  an  audible  whistle. 

The  third  plan  listed  is  theoretically  most  at- 
tractive. A  short-wave  station  is  to  radiate  a 
national  synchronizing  signal,  to  be  used  as  a 
reference  frequency  by  all  broadcasting  stations. 
This  is  accomplished  by  radiating  a  io,ooo-cycle 
note,  impressed  by  modulation  on  a  short-wave 
carrier.  A  receiving  set,  installed  at  each  broad- 
casting station,  would  pick  up  this  signal,  supply 
it  to  a  harmonic  producer  which  multiplies  the 
received  note  to  the  assigned  frequency  of  the 
station.  The  station's  carrier  would  then  be 
adjusted  until  it  zero-beat  with  the  output  fre- 
quency of  the  harmonic  producer.  The  transmit- 
ted synchronizing  signal  cannot  be  higher  than 
10,000  cycles  because  it  must  be  a  multiple  of 
every  frequency  used  as  a  broadcast  carrier. 

The  manual  control  of  a  broadcasting  station's 
frequency  is  difficult  enough  when  a  local  crystal 
oscillator  at  the  station  itself  furnishes  the  ref- 
erence frequency.  But  to  use  for  this  purpose  a 
weak  and  varying  national  synchronizing  signal, 
transmitted  in  most  cases  more  than  a  third  of 
the  way  across  the  country,  is  like  trying  to 
balance  an  egg  on  your  nose.  The  carrier  fre- 
quency of  a  broadcasting  station  is  constantly 
subject  to  slight  variations,  due  to  changing 
temperatures  of  vacuum  tubes,  voltage  changes 
in  the  main  power  supply,  and  the  effect  of  modu- 
lation peaks.  Each  of  these  variations  must  be 
compensated  by  readjustment  of  the  carrier 
frequency.  The  source  of  the  reference  or  com- 
parison frequency  must  therefore  be  perfectly 
stable. 

A    NATIONAL    SYNCHRONIZING    SIGNAL? 

THE  principal  difficulty  with  the  national 
synchronizing  signal  plan  is  that  the  entire 
country  cannot  be  successfully  blanketed  by  the 
output  of  a  single  short-wave  station  at  all  hours 
of  the  day  and  night.  The  received  signal  must 
be  sufficiently  strong  and  stable  to  actuate 
a  harmonic  producer  and  produce  a  steady  ref- 
erence frequency  for  every  broadcasting  station 
in  the  United  States.  The  system  does  not  meet 
the  requirement  of  reliability.  The  cost  of  main- 
taining a  national  synchronizing  station  in  con- 
tinuous operation,  even  if  divided  among  700 
broadcasters,  and  the  rather  elaborate  receiving 
equipment  needed  at  each  station  is  a  serious, 
though  by  no  means  insurmountable,  barrier  to 
ihe  plan. 

1  he  fourth  method  is  the  employment  of  wire 
lines  for  synchronizing  s'  itions.  In  the  case  of 


Energy  from  Station 
Nol 

Energy  from  Station 
No  2 


Resultant  Energy 
Intercepted  by 
Receiving  Sets 


r 


Resultant  Audible 
Heterodyne  Whistle 
in  the  output  ofthe 
Receiver 


WHEN  TWO  STATIONS  INTERFERE 

Station  I  may  be  operating  on  its  correct  fre- 
quency, but  Station  2,  which  we  will  assume 
should  be  on  the  same  frequency,  may  be  slightly 
off  its  assigned  frequency.  A  receiver  tuned  to 
Station  I  also  receives  energy  from  Station  2. 
The  third  curve  shows  what  happens  in  the 
detector  circuit:  the  two  waves  combine  and  in 
the  loud  speaker  there  is  a  heterodyne  whistle, 
constant  in  pitch,  indicated  by  the  fourth  curve. 
If  the  whistle  is  loud  enough,  it  will  completely 
ruin  reception.  Accurate  stabilization  of  the 
carrier  frequencies  of  all  broadcasting  stations 
within  an  accuracy  of  at  least  .05  per  cent,  is 
absolutely  essential  if  reception  is  to  be  free  of 
heterodyne  interference  due  to  this  cause 


chain  broadcasters,  it  might  be  possible  to  use  the 
order  wire  circuit  interconnecting  chains,  but, 
since  chain  circuits  are  set  up  for  only  an  hour  or 
two  each  evening,  the  contribution  to  stability 
which  this  would  afford  is  quite  negligible.  There 
are  not  enough  telephone  wire  facilities  to  spread 
a  national  synchronizing  signal  to  every  city 
where  a  station  exists.  The  cost  of  interconnect- 
ing hundreds  of  stations  would  run  into  several 
million  dollars  annually.  The  economic  burden 
which  wire  synchronization  on  a  national  scale 
would  impose  is  entirely  beyond  the  capacity  of 
the  broadcasting  industry  to  bear. 


LOCATION 
OUTSIDE 

OF  CITY 


LOCATION 
IN  CITY 


18  Per  Cent. 


1 69  Per  Cent. 


1 3  Per  Cent. 


28  Per  Cent. 


45  Per  Cent. 


27  Per  Cent. 


Fair  Service 
Good  Service 
Very  Good  Service 

STATIONS    SHOULD    BE    OUTSIDE   CITIES 

The  drawings  show  the  relative  effectiveness  of 
two  transmitters  of  equal  power,  one  located  in  a 
city  and  the  other  outside.  As  many  listeners  as 
possible  should  be  included  within  the  good 
service  area  of  a  station,  which  is  possible  by 
locating  the  station  outside  of  a  city.  Under  such 
conditions,  60,  per  cent,  are  located  in  the  area  of 
good  service  compared  with  45  per  cent,  in  the 
previous  city  location.  Locating  a  station  outside 
of  a  city  distributes  more  evenly  the  field 
strength  of  the  signals  because  the  absorption 
effect  of  steel  buildings  is  removed.  (Data  from 
Hell  System  Technical  Journal,  Jan.  1927) 


With  respect  to  the  second  problem,  the  syn- 
chronization of  both  program  and  carriers  on  the 
part  of  chain  stations,  many  of  the  considerations 
already  discussed  apply.  The  outstanding  ex- 
ample of  carrier  and  program  synchronization 
has  been  the  successful  simultaneous  operation 
of  WBZ  in  Springfield,  Massachusetts,  and  WBZA 
in  Boston.  A  special  channel  is  utilized  to  trans- 
mit a  synchronizing  signal  so  that  both  stations 
take  their  carrier  frequency  from  the  same 
frequency  source.  Both  stations  invariably 
broadcast  the  same  program.  The  results  of  this 
experiment  have  been  satisfactory  and  the 
question  is  often  asked  why  all  the  stations  of  the 
Red  Network,  for  instance,  do  not  synchronize 
their  carrier  frequencies  in  the  same  way  so  that, 
instead  of  occupying  ten  or  twelve  channels, 
they  would  use  but  one. 

The  task  of  carrier  and  program  synchroniza- 
tion of  WEAF  and  WLW,  for  example,  as  compared 
with  the  synchronization  of  WBZ  and  WBZA, 
presents  some  curious  problems,  the  importance 
of  which  is  not  generally  realized.  In  the  first 
place,  WBZ  and  WBZA  are  separated  by  only 
seventy  miles,  while  WEAF  and  WLW  are  570 
miles  apart.  This  eight-folds  the  wire  leasing 
costs  for  synchronizing  the  latter  two  stations, 
making  a  truly  imposing  financial  burden. 
Secondly,  the  two  stations  do  not  continuously 
and  invariably  radiate  the  same  program.  Were 
they  to  radiate  two  different  programs,  audio- 
frequency distortion  of  both  programs  would  be 
sufficient  to  cripple  the  entertainment  value  of 
both  stations,  even  well  within  their  local  service 
areas.  Third,  since  large  areas  receive  signals 
from  both  WEAF  and  WLW  in  appreciable 
amounts,  the  received  signals  in  such  areas  would 
cause  phase  distortion.  The  reason  that  phase 
distortion  is  not  experienced  more  generally  in 
the  WBZ-WBZA  combination  is  that,  because  of  an 
inexplicable  ether  wall,  there  are  few  points 
where  an  appreciable  signal  is  received  from  both 
stations. 

Considering  that  radio  waves  travel  186,000 
miles  a  second,  it  is  hard  to  conceive  appreciable 
lag  in  the  reception  of  the  same  program  radiated 
simultaneously  from  two  different  stations  at 
varying  distances  from  a  receiving  point.  But, 
even  in  the  hypothetical  case  of  WEAF  and  WLW 
this  lag  may  cause  serious  distortion.  A  listener 
at  Staunton,  Virginia,  where  both  WEAF  and 
WLW  are  received  with  good  volume,  is  approxi- 
mately 272  miles  from  Cincinnati  and  365  miles 
from  Bellmore.  The  distance  from  Bellmore  is 
93  miles  greater  than  the  distance  from  Cin- 
cinnati and  therefore,  theoretically  at  least,  the 
program  from  Bellmore  would  lag  BJff  of  a^ 
second  behind  that  from  Cincinnati.  This  would 
cause  serious  distortion.  Some  frequencies  in 
the  musical  scale  would  be  exaggerated  and 
others  reduced  in  intensity. 

Experience  with  the  reception  of  several 
signals  from  the  same  station,  through  the  effect 
of  reflection  and  the  influence  of  bodies  of  water 
resulting  in  phase  differences,  offers  valuable 
evidence,  tending  to  confirm  the  distorting 
effect  of  synchronized  chain  broadcasting  where 
the  receiver  responds  appreciably  to  signals  from 
more  than  one  broadcasting  station. 

Ordinarily,  the  reception  of  two  or  three 
signals  from  the  same  station  does  not  seriously 
affect  quality  because  one  of  the  signal  sources 
usually  predominates  over  the  others  sufficiently 
to  make  their  influence  negligible.  But  there  are 
many  known  cases  where  phase  distortion  ac- 
counts for  the  poor  quality  with  which  high- 
grade  stations  are  heard  in  some  areas.  \\  hen 
WEAF  broadcast  from  Walker  Street,  several 
years  ago,  listeners  in  Pelham,  New  York,  but 
16  miles  airline  distance  from  the  transmitter, 
complained  that,  even  with  the  best  Of  recei\ers. 


8 


RADIO  BROADCAST 


MAY,  1928 


only  a  weak  and  distorted  signal  could  be  re- 
ceived. A  thorough  investigation  with  loop  re- 
ceivers and  field  strength  measuring  equipment 
revealed  that  two  signals  from  WEAF,  apparently 
coming  in  from  two  different  directions  and,  at 
some  points,  exactly  180  degrees  out  of  phase, 
tended  to  cancel  each  other.  Similar  effects  would 
be  experienced  when  two  stations  radiate  identi- 
cal programs  on  the  same  channel. 

If  a  chain'of  twenty  stations  were  synchron- 
ized, the  resultant  reception,  at  all  points  beyond 
the  high-grade  service  range  of  the  synchronizing 
stations,  would  at  least  lack  that  clearness  and 
purity  of  tone  which  characterizes  modern  broad- 
casting and  might  be  sufficiently  confused  to  be 
almost  unrecognizable.  Because  of  this  con- 
sideration, desirable  synchronization  of  chain 
programs  is  limited  to  stations  widely  separated 
geographically  so  that  no  listener  is  within  the 
practical  range  of  more  than  one  synchronized 
station. 

CHAIN    STATION    SYNCHRONISM 

THE  practical  application  of  synchronization 
of  chains  is  thereby  limited  to  the  establish- 
ment of  two  or  three  groupings  per  chain  rather 
than  placing  all  the  members  of  a  chain  on  a 
single  channel.  This  would  not  effect  radical 
saving  of  cleared  channels,  a  maximum  of  four 
or  five  for  each  chain  being  possible. 

A  further  barrier  to  extended  chain  synchroni- 
zation is  the  fact  that  it  can  conserve  channels 
only  if  the  stations  involved  broadcast  chain 
programs  exclusively.  Since  most  of  the  subscrib- 
ing stations  use  chain  programs  only  occasion- 
ally, an  hour  or  two  each  evening  at  the  most, 
permanent  assignments  to  synchronized  channels 
is  now  impossible.  The  cost  of  wire  lines  and 
chain  features  is  altogether  too  high  to  require 
subscribers  to  chain  programs  to  utilize  only 
chain  programs.  Yet,  only  under  those  condi- 
tions, would  chain  synchronization  effect  any 
economy  of  channels.  Most  chain  stations  broad- 
cast local  programs  and  perform  local  services 
during  a  majority  of  their  broadcasting  time. 
These  services  would  have  to  be  discontinued  or 
transferred  to  minor  stations  under  any  plan  of 
widespread  chain  program  synchronization. 

Considering  that  the  problem  is  to  find  com- 
fortable room  for  nearly  700  stations  in  a  band 
of  89  channels,  reliance  upon  the  single  measure 
of  chain  station  synchronization  does  not  offer 
any  promise  of  real  relief,  even  if  the  difficulties 
cited  could  be  overcome  immediately. 

A  trend  of  development  which  holds  some 
promise  is  improvement  in  the  permissible  per- 
centage of  modulation  without  resultant  distor- 
tion. This  is  the  third  general  measure  of  relief 
given  at  the  beginning  of  this  article.  Its  effect 
is  to  increase  the  percentage  of  the  high-grade 
service  area  to  the  total  carrier  interference  range 
area.  The  experimental  fifty- kilowatt  transmitter 
at  Whippany.  maintained  by  the  Bell  Labora- 
tories, utilizes  a  new  method  of  combining  carrier 
with  program  signal,  said  to  effect  one  hundred 
per  cent,  modulation.  While  the  results,  so  far  as 
increased  service  range  for  a  given  carrier  power 
is  concerned,  are  not  startling,  they  are,  never- 
theless, appreciable.  The  engineering  ideal  to 
be  attained  in  this  direction  is  that  the  carrier 
shall  cease  to  radiate  at  the  edge  of  the  station's 
high-grade  service  area.  The  problem  of  setting 
up  an  intense  wave  motion  of  any  kind  and  mak- 
ing it  cease  abruptly  at  the  limit  of  its  usefulness 
is  a  tremendous  challenge  to  engineering  in- 
genuity. In  radio  transmission,  there  is  room  for 
so  much  improvement  in  reducing  the  ratio  of 
carrier  spread  to  useful  service  range  that  some 
progress  in  this  direction  may  be  hoped  for. 
But  that  this  development  will  have  material 
bearing  in  the  present  situation  is  not  within 


the  expectation  of  the  most  sanguine  workers  in 
this  field  of  research. 

Considering  the  immediate  possibilities  of  all 
the  proposed  measures  of  relief,  none  holds 
greater  promise  than  the  development  of  high- 
precision  crystal  oscillators  with  accurate  tem- 
perature control.  Realizing  the  value  of  a  source 
of  constant-frequency  oscillation,  many  labora- 
tories have  been  concentrating  on  this  problem 
during  the  last  few  months.  The  writer  has  seen, 
in  the  development  stage,  a  new  type  of  quartz 
crystal  precision  oscillator  for  broadcasting  sta- 
tions which  will  probably  be  marketed  by  the 
R.  C.  A.  This  device  will  consist  of  two  ac- 
curately ground  and  matched  quartz  crystals 
mounted  in  a  constant  temperature  chamber. 
The  temperature  is  kept  constant  by  means  of  a 
thermostat  and  maintained  at  a  given  setting 

WIDTH  OF  CHANNEL  WIDTH  OF  CHANNEL 

CARRIER  PLUS  SIDE  BANDS   CARRIER  PLUS  SIDE  BANDS 

Station  Station 
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"CARRIERS"  AND  "SIDEBANDS" 

Stations  assigned  to  adjacent  broadcasting  chan- 
nels transmit  on  carrier  frequencies  differing  by 
10,000  cycles.  When  programs  are  transmitted, 
two  sidebands  are  produced  which  introduce 
into  the  transmitted  wave,  frequencies  up  to 
5000  cycles  above  and  5000  cycles  below  the 
carrier  frequency;  the  station  therefore  uses  a 
band  of  frequencies  10,000  cycles  wide.  The 
left  sketch  shows  the  frequency  bands  used  by 
two  adjoining  stations.  The  two  carrier  fre- 
quencies differ  by  10,000  cycles;  the  sidebands 
meet  each  other  but  do  not  overlap.  This  holds 
true  when  two  adjacent  stations  hold  exactly 
to  their  assigned  frequency.  If  either  station 
varies,  the  condition  shown  at  the  right  obtains, 
where  we  have  assumed  that  one  station  has 
wandered  from  its  frequency  to  the  extent  of 
4000  cycles  (4  kc.)  deviation.  This  leaves  the 
carrier  separation  between  the  two  only  6000 
cycles  (6  kc.).  Then,  in  the  receiver  output,  we 
would  hear  a  6ooo-cycle  note,  which  may  be 
loud  enough  to  ruin  reception.  Interaction  be- 
tween the  two  sidebands  of  the  stations — shown 
on  the  shaded  portion  of  the  diagram — also 
occurs 


by  means  of  this  thermostat,  checked  by  a 
thermometer.  A  suitable  heating  coil  is  also 
mounted  in  the  constant  temperature  chamber. 
The  two  crystals,  supplied  with  this  oscillator, 
may  be  ground  to  any  one  frequency  in  the 
band  of  from  550  to  1500  kilocycles.  A  small 
selector  switch  is  arranged  to  select  either  of  the 
two  crystals.  Should  one  of  the  crystals  fail  dur- 
ing the  operation  of  a  broadcasting  station,  it  is 
only  necessary  to  throw  this  selector  switch 
which  removes  the  defective  crystal  and  cuts  in 
the  spare  crystal,  which  will  be  at  the  right 
temperature  to  start  operation  immediately. 

The  oscillator  circuit  will  consist  of  a  vacuum 
tube  and  coil  system,  the  electrical  constants  of 


which  have  been  very  carefully  determined  with 
a  view  to  being  suitable  to  work  with  the  quartz 
crystals.  A  monitoring  receiver,  comprising  a 
suitable  detector  and  two  stages  of  audio- 
frequency amplification,  in  a  separate  box,  has 
also  been  designed  for  use  in  connection  with  the 
quartz  crystal  precision  oscillator.  When  these 
two  boxes  (the  quartz  crystal  oscillator  and  the 
monitoring  receiver)  are  used  in  conjunction,  a 
loud  speaker  may  be  connected  to  the  output  of 
the  last  stage  of  audio-frequency  amplification 
and  the  quartz  crystal  frequency  beat  against  the 
carrier  of  the  broadcasting  station.  Special 
precautions  will  be  taken  to  emphasize  the  low 
frequencies  so  that  the  zero-beat  note  will  be 
heard  at  its  greatest  efficiency. 

No  definite  claims  have  yet  been  made  as  to 
the  stability  of  this  device,  but  there  is  no  ques- 
tion that  two  stations,  operating  on  the  same 
channel,  both  employing  the  device,  will  not 
heterodyne  each  other  seriously.  It  should  elimi- 
nate the  high  pitched  squeal  and  that,  alone,  will 
justify  its  installation.  It  is  not  unreasonable 
to  expect  that,  with  continued  improvement 
and  experience  with  precision  quartz  crystal 
oscillators,  complete  carrier  synchronization 
will  ultimately  be  made  possible. 

NEW   METHODS   OF   TRANSMISSION 

THIS  summary  would  be  incomplete  if 
mention  were  not  made  of  several  proposed 
new  methods  of  transmission,  claimed  to  reduce 
the  width  of  the  channel  required  by  a  broad- 
casting station.  These  methods  are  frequently 
mentioned  in  public  statements,  issued  as  possi- 
ble measures  of  relief  by  persons  who  must  know 
the  objections  to  their  adoption  in  the  broad- 
cast band.  One  is  single  side-band  transmission, 
accomplished  by  suppression  of  the  carrier  and 
one  side-band,  as  utilized  in  practice  in  the 
transatlantic  telephone.  It  has  the  vital  objec- 
tion that  its  adoption  is  predicated  upon  scrap- 
ping every  transmitting  and  receiving  equip- 
ment in  the  country.  The  broadcast  receiver 
necessary  to  pick  up  single  side-band  trans- 
mission is  expensive  and  delicate.  One  of  its 
elements  is  an  oscillator  which  must  be  adjusted 
to  within  ten  or  fifteen  cycles  of  the  assigned 
frequency  of  the  station  to  be  received,  in  order 
to  supply  the  missing  suppressed  carrier.  To 
reequip  every  broadcast  listener  with  a  suitable 
receiver  under  this  system  would  cost  the  public 
not  less  than  half  a  billion  dollars. 

Another  suggestion  along  these  lines  is  the 
adoption  of  a  new  system  of  frequency  modula- 
tion. For  this  has  been  claimed  the  extraordinary 
virtue  of  accommodating  simultaneously  be- 
tween one  and  two  thousand  broadcasting  sta- 
tions in  the  present  band.  The  basic  principle  of 
the  system  is  that  the  carrier  frequency  is  shifted 
up  and  down  according  to  the  desired  audio 
signal  to  be  transmitted.  The  receiving  set  is 
tuned  with  extreme  sharpness  so  that  the  shifting 
carrier  causes  varying  energy  to  actuate  the 
receiving  set  by  reason  of  the  detuning  effect. 
This  sytem  would  also  require  the  scrapping  of 
all  receiving  sets,  unless  the  carrier  is  shifted 
over  so  wide  a  scale  that  no  economy  of  channels 
is  effected.  The  contention  is  also  raised  that  a 
shifting  carrier  sets  up  numerous,  harmonics  so 
that  the  theoretically  narrow  band  occupied 
by  the  frequency  modulated  carrier  would  prove 
to  be  in  practice  no  narrower  than  that  used  by 
broadcasting  .stations  operating  under  the 
present  simple  methods  of  modulation. 

A  most  exhaustive  study  of  the  entire  subject 
will  lead  inevitably  to  the  conclusion  that  prog- 
ress in  increasing  the  capacity  of  the  broadcast- 
ing band  will  be  steady  but  that  no  radical 
developments,  sufficient  to  offer  a  complete 
solution  to  the  present  problem,  are  in  sight. 


IME.W.S'   AND  INimPUnATION  OK  r.iiUWNT  UAhlQ  EVHM'I'.S 

Why  the  Persistent  Cry  of  Monoply? 


THE  struggle  now  shaking  the  foundations 
of  the  radio  industry  has  long  been  brew- 
ing. On  one  hand  is  assembled  a  group  of 
militant  independent  manufacturers,  vigorously 
attacking  an  alleged  monopoly  whose  grasping 
tentacles  reach  into  every  branch  of  the  radio 
field;  on  the  other  hand,  the  radio  mouthpiece 
of  vast  electrical  interests,  claiming,  with  injured 
innocence,  that  it  was  born  out  of  patriotic  mo- 
tives and  possesses  its  imperalistic  power  over 
the  radio  industry  by  virtue  of  its  widespread  and 
proper  patent  rights.  Drawn  into  this  conflict  are 
the  Federal  Courts,  the  Federal  Trade  Com- 
mission, Congress,  and  the  Federal  Radio 
Commission. 

The  consequences  of  this  struggle  may  be  far- 
reaching.  So  great  is  the  patent  strength  of  the 
combination  that  little  reliance  is  placed  upon 
upsetting  the  validity  of  enough  patents  which  it 
holds  to  free  the  industry  of  its  domination.  Nor 
is  there  any  vast  sum  being  spent  in  research  to 
develop  non-infringing  vacuum  tubes  and  as- 
sociated circuits.  Instead,  attack  has  been  made 
upon  the  methods  used  in  taking  advantage  of 
its  patent  position  and  upon  the  fundamentals 
of  the  patent  itself. 

Several  bills  before  Congress  propose  drastic 
revision  in  the  powers  conferred  upon  all  patent 
holders;  one,  for  example,  seeks  to  make  revoca- 
tion of  patents  the  penalty  for  violation  of  anti- 
trust laws  so  that  companies  conducting  research 
and  promoting  progress  will  suffer  more  severely 
than  those  which  simply  copy  designs  and  in- 
fringe patents.  Another  bill  proposes  that  pat- 
ents applying  to  vacuum  tubes  shall  not  confer 
upon  their  holders  the  same  rights  which  apply 
to  all  other  articles,  a  plain  discrimination  against 
one  industry. 

Another  line  of  attack  is  through  the  Federal 
Radio  Commission.  The  commission  is  severely 
criticized  by  Congress,  to  which  it  reports,  and 
by  hostile  station  owners,  for  the  privileges  ex- 
tended to  the  chain  stations,  partly  owned  by 
the  combination.  Bills  proposing  equal  geo- 
graphic distribution  of  broadcast  transmitters 
are  being  written,  requiring  the  destruction  or 
curtailment  of  useful  and  popular  broadcasting 
services.  The  operation  of  such  a  law  would  in- 
evitably require  power  reductions  on  the  part  of 
WEAF,  wjz,  WGY,  and  KDKA,  all  N.  B.  C.  stations. 
No  avenue  is  being  overlooked  to  injure,  directly 
or  indirectly,  any  and  every  activity  of  the  com- 
bination. 

Let  us  view  the  situation  sanely.  A  wave  of 
resentment  has  arisen  against  the  power  of  the 
Radio  Corporation  of  America  and  the  huge 
electrical  interests  backing  it.  This  power  is 
based  upon  the  ownership  of  patents,  in  them- 
selves a  legal  monopoly.  The  restrictions  imposed 
by  patent  holders  are  escaped  either  by  abandon- 
ing the  field,  paying  royalties,  or  devising  new 
methods  which  do  not  infringe.  Many  companies 
in  the  radio  industry  have  elected  to  pay  royal- 
ties. There  is  no  indication  that  any  of  the  un- 
licensed independents  are  making  any  real  effort 
to  devise  non-infringing  designs.  They  elect  to 
follow  none  of  the  three  customary  alternatives. 

Politics  have  further  clouded  matters  in  a  fog 
of  flaming  oratory.  Bills  are  proposed,  with  the 


intention  of  injuring  the  Radio  Corporation  of 
America,  which,  if  passed,  will  accomplish  that 
objective,  but  will  also  mutilate  both  the  present 
broadcasting  structure  and  the  entire  patent 
structure  upon  which  American  industry  has 
been  built.  The.  Radio  Corporation  of  America 
should  be  punished  for  any  crimes  of  which  it  is 
guilty,  but  it  would  be  unfortunate  if  unwise 
legislation  were  enacted  in  the  current  anxiety 
to  inflict  punishment. 

The  foundations  for  the  present  situation  were 
laid  shortly  after  the  war.  American  communica- 
tions had  been  greatly  hampered,  both  during 
and  after  the  period  of  neutrality,  by  foreign 
censorship  and  foreign  ownership  of  cables  and 
long-distance  radio  communications.  Naval 
officials  desired  the  establishment  of  an  American 
owned  transoceanic  network  and  an  American 
radio  industry  so  that  channels  of  communica- 
tion and  sources  of  supply  for  war  needs  would 
always  be  available.  No  one  company  had  access 
to  a  sufficient  number  of  patents  to  enable  it  to 
conduct  a  profitable  transoceanic  radio  service 
or  even  to  manufacture  modern  vacuum-tube 
transmitting  and  receiving  apparatus. 

With  the  encouragement  of  high  naval  officials, 
the  Radio  Corporation  of  America  was  formed 
in  1919.  It  was  given  rights,  in  a  patent  pool 
comprising  the  principal  radio  patent  holders, 
to  conduct  transoceanic  services  and  marine 
communication  and  also  to  sell  transmitting  and 
receiving  apparatus  to  the  handful  of  amateurs 
then  operating.  The  pool  consisted  of  the  Amer- 
ican Telephone  &  Telegraph  Company  and  its 
subsidiary,  the  Western  Electric  Company,  the 
General  Electric  Company,  the  Westinghouse 


RADIOMARINE  CORPORATION  ORGANIZED 
The  ship-to-shore  marine  radio  communications 
of  the  Radio  Corporation  of  America  were  trans- 
ferred to  a  new  subsidiary,  the  Radiomarine 
Corporation  with  which  was  combined  the  In- 
dependent Wireless  Company.  Charles  J. 
Pannill,  former  president  of  the  Independent,  is 
now  vice-president  and  general  manager  of 
Radiomarine  and  J.  P.  Duffy,  for  years  superin- 
tendent of  the  New  York  division  of  RCA 
marine,  has  been  appointed  superintendent  of 
operations.  Mr.  Duffy  is  shown  above 


Electric  &  Manufacturing  Company,  and  the 
Wireless  Specialty  Apparatus  Company.  Each 
company  threw  their  radio  patents  into  the 
pool  and  received  license  under  all  the  patents, 
each  for  use  in  a  particular  and  limited  field  of 
activity.  The  fundamental  objective  of  the  com- 
bination sought  by  the  Navy  was  promptly 
accomplished.  The  world-wide  communication 
system  came  into  being.  Had  this  been  the 
only  result  of  this  pooling  arrangement,  there 
would  be  no  conflict  to-day. 

Radio  broadcasting  came  in  an  avalanche  of 
public  enthusiasm  in  1920  and  1921.  It  is  obvious 
to  anyone  who  has  read  the  original  agreement, 
upon  which  the  patent  pool  is  based,  that  broad- 
casting was  not  contemplated  when  the  pool 
was  formed.  But  the  patent  structure  which  was 
thus  built  up  has  established  an  almost  impreg- 
nable domination  of  the  radio  industry.  Con- 
sidering the  immense  research  facilities  of  the 
group  and  the  important  patents  which  its  vari- 
ous members  have  purchased,  it  is  in  a  position 
to  maintain  that  hold,  unless  its  patent  rights 
are  abridged  or  modified. 

At  the  beginning  of  the  radio  boom  seven 
years  ago,  few  of  the  group's  radio  patents  had 
been  adjudicated.  An  independent  industry  grew 
up  and  flourished  in  total  disregard  of  these 
patents.  A  few  gestures  were  made  by  the  group 
to  make  known  its  patent  holdings,  such  as  send- 
ing infringement  warnings  to  manufacturers  by 
registered  mail  regarding  the  Pickard  crystal 
patents,  but  no  effort  was  made  to  make  the 
public  conscious  of  the  importance  of  the  poo], 
its  research  facilities,  and  the  patents  which  it 
held.  Suits  were  filed  which  are  only  now  being 
finally  settled. 

With  recent  adjudications,  all  of  the  large 
producers,  representing  about  three  fourths  of 
the  industry's  volume,  have  become  licensees  of 
the  group.  The  remainder  have  been  unable  or 
unwilling  to  meet  the  license  terms,  with  their 
minimum  annual  royalty  guarantee  of  $100,000. 
The  independent  vacuum-tube  industry  has 
been  virtually  destroyed  by  the  effects  of  one  of 
the  clauses  of  the  license  contract  which  requires 
that  all  licensed  radio  sets  be  equipped  with  tubes 
sold  by  the  R.C.  A. or  Cunningham,  a  subsidiary. 
This  clause  has  been  adjudged  as  a  case  of  re- 
straint of  trade  under  the  Clayton  Act.  The 
R.  C.  A.'s  justification  might  be  among  other 
things,  that  no  one  can  make  tubes  without 
infringing  their  patents  (adjudicated  and  un- 
adjudicated),  and  hence  there  is  no  legal  com- 
petition. 

This,  briefly,  and  stripped  of  many  ramifica- 
tions, is  the  background  of  the  situation.  The 
combination  was  formed  with  a  useful  and  pa- 
triotic purpose  which  has  been  successfully  ac- 
complished. Its  existence  was  also  instrumental 
in  initiating  the  first  permanent  broadcasting 
and,  more  recently,  in  making  possible  a  source 
of  a  comprehensive  license  to  manufacture  radio 
receiving  sets  without  infringement  of  any  but 
a  few  patents  held  outside  of  the  group.  Several 
members  of  the  combination  are  responsible  for 
vitally  important  research  work,  contributing  to 
the  modern  standard  of  radio  reproduction. 

Strongcompanies  anddominent  groupsexist  in 


10 


RADIO  BROADCAST 


MAY,  1928 


every  important  field  of  industry.  But  in  none  is 
the  dominant  group  so  generally  disliked  and  so 
freely  criticized.  Mention  of  the  General  Motors 
to  an  independent  automotive  engineer  or  motor 
car  wholesaler  does  not  have  the  effect  of  ruining 
his  digestion  or  moving  him  to  profanity.  Why 
all  this  resentment  against  the  radio  combina- 
tion? 

The  Radio  Corporation  of  America  is  singu- 
larly devoid  of  public  relations  sense.  1 1  has  never 
effectively  set  itself  to  the  task  of  winning  public 
goodwill.  Only  when  under  attack  does  it  offer 
belated  explanations.  It  conducts  its  affairs  in  a 
dictatorial  manner,  deciding  for  itself  what  is 
good  for  it  and  what  is  good  for  the  entire  in- 
dustry. It  regards  the  interests,  but  apparently 
not  the  opinion,  of  the  public.  The  severest  pen- 
alties are  imposed  by  the  court  of  public  opinion. 

We  must  distinguish  between  publicity  and 
public  relations.  Publicity  is  a  matter  of  releas- 
ing information  to  the  press.  In  this  respect  the 
R.  C.  A.  is  highly  efficient.  It  issues  publicity 
material  copiously.  Public  relations  involve 
every  relationship  with  those  outside  a  company's 
personnel,  not  merely  relations  with  the  press. 
The  building  up  of  satisfactory  public  relations 
requires  that  every  act,  however  small,  be  con- 
sidered in  the  light  of  public  understanding  and 
interpretation. 

It  may  be  legal  to  collect  royalties  based  on 
the  gross  business  of  a  licensee,  but  how  will  the 
public  react  to  the  knowledge  that  one  manu- 
facturer, making  a  cheap  table  model  radio  set, 
pays  three  or  four  dollars  royalty  on  each  set  he 
makes,  while  another,  using  the  same  patents  in 
the  same  way,  pays  fifteen  or  twenty  dollars 
because  his  set  is  of  high  quality  and  is  housed 
in  a  piece  of  fine  furniture?  How  will  the  public 
feel  when  it  learns  that  R.  C.  A.  patent  royalties 
have  been  sufficiently  large  to  add  greatly  to  the 
cost  of  producing  radio  sets  and  to  make  the 
operations  of  some  of  the  most  successful  inde- 
pendent companies  almost  profitless? 

An  early  adjustment  of  the  present  situation 
must  be  effected,  lest  it  cause  the  passage  of 
legislation  detrimental  to  all  patent  holders.  Any 
law  which  makes  a  patent  less  valuable  and  offers 
less  protection  to  the  owner  of  a  patent  will 


discourage  scientific  research  and  rob  the  inde- 
pendent inventor  of  his  incentive  to  devote  him- 
self to  progress.  Unless  considerable  forbearance 
and  cool  judgment  is  displayed  by  all  the  parties 
involved  in  the  present  controversy,  the  only 
possible  outcome  is  legislation  which  will  per- 
manently weaken  our  patent  structure.  Aroused 
public  opinion  may  exact  too  great  a  penalty, 
unless  the  patent  holding  group  be  guided  by 
more  of  the  spirit  of  live  and  let  live. 

Radio  Laughs  at  Wired  Wireless 

OUR  contemporary,  Radio  Retailing,  leads 
off,  in  a  recent  issue,  with  a  stirring  edi- 
torial to  the  effect  that  the  radio  industry 
can  no  longer  "laugh  off"  the  approach  of  wired 
wireless.  It  states  that  the  program  services, 
which  the  electric  companies  will  soon  pour  into 
American  homes  via  the  power  lines,  will  be 
superior  in  quality  to  "space"  broadcasting  and 
hints  that  radio  will  have  difficulty  in  competing 
with  them.  The  publication  solemnly  warns  the 
radio  industry  to  prepare  for  the  competition 
of  wired  wireless. 

Because  of  the  well-earned  reputation  of  our 
contemporary,  these  editorial  remarks  have 
created  some  uneasiness  in  the  radio  trade.  It  is 
our  view,  however,  that  we  can  "laugh  off" 
wired  wireless  competition  for  many  a  year.  In 
fact,  we  very  gravely  doubt  that  the  future  of 
wired  wireless  is  as  rosy  as  Radio  Retailing  be- 
lieves it  to  be. 

If  the  electric  power  companies  can  find  better 
symphony  orchestras  than  the  Philharmonic 
and  the  New  York  Symphony,  more  important 
prizefights  than  the  Dempsey-Tunney,  better 
bands  than  the  Marine  Band  and  the  Goldman, 
greater  artists  than  Jeritza,  Mary  Garden,  Galli 
Curci,  John  McCormack,  Gigli — oh  well,  what's 
the  use  of  continuing — anything  they  can  un- 
earthwill  quickly  be  recruited  to  the  broadcasting 
field.  The  power  companies  will  require  as 
elaborate  and  as  expensive  transmission  equip- 
ment as  do  broadcasting  stations  serving  an  equal 
area.  There  is  no  reason  to  believe  that  the  wired 
wireless  company  can  secure  talent  at  a  lower 
cost  than  can  broadcasting  companies.  They 


A    SAMPLE    OF    FACSIMILE    TRANSMISSION    BY    THE    KORN    SYSTF.M 


cannot  claim  better  transmission  quality  because 
power  lines  also  have  their  share  of  atmospheric 
noises  and,  in  addition,  current  surges  and  dis- 
turbances which  are  fully  as  great,  if  not  greater, 
than  those  with  which  radio  contends.  They 
cannot  claim  more  faithful  reproduction  because 
radio  now  encompasses  practically  all  the  fre- 
quencies heard  by  the  human  ear.  Wired  wireless 
has  no  advantage  over  radio  in  cost  of  program 
and  technical  operations  or  in  reproduced  result. 

The  most  important  claim,  made  by  the  sup- 
porters of  wired  wireless,  is  that  it  will  not  put 
forth  publicity  programs.  Wire  broadcasting  will 
derive  its  revenue,  not  from  transmission,  but 
from  reception.  The  consumer  will  pay  directly 
at  a  rate  probably  ranging  between  three  and  ten 
or  twelve  dollars  a  month,  depending  upon 
whether  he  is  content  to  use  headphones  or 
wishes  high-grade  loud  speaker  reception.  We 
hazard  the  prediction  that  the  electric  power 
companies  will,  sooner  or  later  (and  probably 
sooner),  yield  to  the  temptation  of  making  oc- 
casional remarks  about  electrical  appliances, 
good  lighting  and  a  few  other  things  which  will 
promote  the  sale  of  electrical  apparatus  and  in- 
crease current  consumption.  The  monthly  wire 
broadcasting  toll  will  be  a  much  more  serious 
obstacle  to  spreading  wired  wireless  than  is  the 
publicity  accompanying  commercial  radio  pro- 
grams to  the  growthof  the  broadcasting  audience. 

I  he  American  public  is  not  accustomed  to 
paying  for  something  which  it  can  secure  without 
direct  payment.  The  monthly  payment  feature 
of  wired  wireless  will  confine  its  market  very 
largely  to  public  places,  such  as  restaurants,  hotel 
lobbies,  and  railroad  station  waiting  rooms.  That 
element  of  the  consuming  public  which  considers 
programs  coming  over  an  electrical  circuit  so 
superior  to  radio  reception  that  it  is  waiting  for 
the  coming  of  wired  wireless  is  not,  and  never  has 
been,  a  prospect  for  radio  sets. 

We  believe  our  contemporary  has  considerably 
exaggerated  the  possibilities  of  wired  wireless. 
The  radio  industry  has  little  or  nothing  to  fear 
from  its  competition.  Wired  wireless  will  serve 
a  field  peculiar  to  itself  and  has  a  valuable  mission 
to  perform  but,  in  so  doing,  it  will  not  be  a  serious 
or  dangerous  competitor  to  the  radio  industry. 

Congress  Dabbles  with  the  Radio 
Situation 

CONGRliSS  has  been  intensely  busy  tin- 
kering with  the  radio  situation  during 
the  last  few  months.  The  House  Com- 
mittee on  Marine  and  Fisheries,  the  Senate 
Committee  on  Interstate  Commerce,  and  the 
Senate  Patent  Committee  have  been  the  scene 
of  endless  hearings,  inquiring  into  every  phase 
of  broadcasting  and  radio  manufacturing.  The 
result,  at  the  time  of  writing,  has  been  to  paralyze 
the  Federal  Radio  Commission  into  almost 
complete  inactivity  and  to  confuse  the  entire 
situation  with  a  riot  of  rabid  opinions. 

It  is  likely  that  some  form  of  legislation  will 
be  passed  by  the  time  this  editorial  appears, 
presumably  extending  the  life  of  the  Radio  Com- 
mission for  another  year.  The  opposition  to  this 
course  is  based  largely  on  a  desire  to  embarrass 
Secretary  Hoover  with  the  radio  situation  by  the 
automatic  operation  of  the  unamended  Radio 
Act  of  1927.  If  the  situation  does  revert  to  his 
jurisdiction,  he  must  make  some  progress  with  it 
and.  in  so  doing,  will  incur  the  enmity  of  poli- 
ticians in  the  areas  affected.  Thus  Congress, 
unable  to  help  the  radio  situation  by  intelligent 
legislation,  proceeds  to  use  it  to  its  own  political 
advantage. 

Nothing  of  particular  novelty  has  been  re- 
vealed in  any  hearings  and  only  one  statement  of 
importance  has  been  made  A  bill  has  been  pro- 


MAY,  1928 


RADIO  PICTURE  AND  TELEVISION  PROGRESS 


11 


posed  to  clarify  the  equitable  distribution  of 
broadcasting  service  clause  of  the  Radio  Act  of 
1027  The  total  wattage  of  broadcasting  stations 
in  the  southern  district  is  less  than  that  of  the 
largest  single  station  in  the  northeastern  district. 
The  Federal  Radio  Commission  is  being  blamed 
for  this  situation  and  is  charged  with  discrimina- 
tion against  the  south.  To  bring  about  a  modi- 
fication, the  bill  proposes  that  the  total  wattage 
of  the  five  districts  shall  be  equalized. 

Commissioner  Caldwell  responded  to  this 
destructive  suggestion  by  pointing  out  that  the 
principal  program  sources  of  the  entire  country 
would,  by  the  operation  of  such  a  provision,  be 
required  to  suffer  substantial  power  cuts,  de- 
priving immense  rural  populations  of  their  favor- 
ite program  services.  There  are  neither  stations 
nor  frequency  space  sufficient  to  bring  up  the 
total  wattage  in  the  less  progressive  areas  (speak- 
ing only  from  the  broadcast  transmission  stand- 
point), and,  consequently,  the  only  possible  way 
in  which  to  observe  the  proposed  law  would  be 
to  reduce  the  power  of  every  station  in  the  New 
York  district  by  eighty  per  cent.,  or  eliminate 
a  large  number  of  medium  and  high-power 
stations.  Many  of  the  politicians  were  highly  ir- 
ritated by  Commissioner  Caldwell's  succinct 
exposition  of  the  situation  but,  so  forceful  was  his 
logic  that  the  only  answer,  so  far  made,  has  con- 
sisted of  pointed  and — it  seems  to  us — unjusti- 
fied insinuations  about  the  Commissioner's 
susceptibility  to  the  influence  of  the  great  broad- 
casters. 

Commissioner  Caldwell  is  to  be  commended 
for  stating  the  facts  so  plainly  and  having  the 
courage,  at  this  time,  to  stick  to  the  truth  even 
though  it  be  favorable  to  the  viewpoint  of  the 
\.  B.  C.  Political  wisdom  dictates  a  different 
attitude  but  he  is  swayed  only  by  a  desire  to 
serve  the  listener. 

The  only  other  activity  of  the  Commission 
has  been  the  issuance  of  a  formidable  list  of  fre- 
quency and  power  changes  by  Commissioner 
l.aFount,  affecting  stations  on  the  Pacific  Coast. 
These  changes  promise  to  clear  up  many  existing 
heterodynes.  It  seems  quite  apparent,  at  this 
writing,  that  congressional  bungling  will  prolong 
the  present  unsatisfactory  radio  situation  for 
another  year. 

HAIKU    ThLEVISlON    APPARATUS    ON    SALF- 

1)RFSS  dispatches  from  London  announce 
that  Selfridge's  is  selling  Baird  television 
outfits  at  a  price  of  thirty-two  dollars  per  set. 
Investigation  reveals,  however,  that  this  equip- 
ment consists  only  of  the  parts  for  building  a 
shadowgraph  transmitting  outfit.  The  amateur 
transmitting  enthusiast  can  send,  at  his  home,  ;i 
moving  hand  or  a  shadow  made  by  a  cardboard 
figure  held  before  the  outfit.  The  cost  of  the 
receiver  parts,  to  be  marketed  later,  will  be  ap- 
proximately the  same.  The  shadowgraph  offers 
a  field  for  entertaining  home  experiments  and  it 
should  promote  interest  in  the  problems  of  tele- 
vision. 

As  to  the  commercialization  of  television  in  the 
United  States,  a  statement  made  by  David 
Sarnoff  of  the  Radio  Corporation  of  America, 
before  the  New  York  Electrical  League,  is 
significant.  He  is  quoted  in  the  press  as  saying: 
"We  will  hear  much  more  about  these  develop- 
ments within  the  next  year.  My  guess  is  that, 
within  five  years,  they  (television  receivers)  will 
be  as  much  a  part  of  our  life  as  sound  broad- 
casting is  now." 

An  unnamed  representative  of  the  R.  C.  A. 
is  quoted  in  the  New  York  Times,  when  ques- 
tioned as  to  how  soon  the  Alexanderson  still 
picture  transmission  apparatus  will  be  placed  on 
the  market,  as  follows:  "Oh.  it  will  be  a  long 


•*-Ua 

.-•-.-., 

- 


GERMAN      POLICE     USE     THE     KORN 
PICTURE    SYSTEM 

In  recent  months,  the  Korn  picture  transmitting 
system  has  been  adopted  for  regular  use  by  the 
German  police.  The  illustration  shows  a  sample 
of  the  received  picture.  Average  transmitting 
time  for  a  picture  is  said  to  be  2j  minutes 


time.  Look  at  the  apparatus.  It  is  top  cumber- 
some. It  is  only  in  experimental  form." 

Considering  the  great  number  of  years  that 
photo  transmission  has  been  the  subject  of  ex- 
periment both  here  and  abroad  and  the  success 
obtained  by  such  pioneers  as  Korn,  Jenkins 
and  Baird,  and  the  recent  successes  of  the  Bell 
Laboratories  and  Alexanderson,  it  is  surprising 
that  picture  broadcasting  is  so  slow  in  becoming 
a  supplement  to  tone  broadcasting. 

PICTURE  BROADCASTING  MUST  CONTAIN  NO  "ADS" 

MR.  DAVID  CASEM,  Radio  Editor  of  the 
New  York  Telegram,  pointed  out  editori- 
ally recently  that  numerous  commercial  broad- 
casters are  already  considering  ways  and  means 
in  which  they  can  use  picture  broadcasting.  He 
points  out  that,  if  picture  transmission  is  used  to 
distribute  miniature  billboards  in  the  home,  its 
growth  will  be  stifled  at  the  outset.  The  public 
is  not  going  to  buy  picture  receiving  apparatus 
in  order  to  have  itself  exploited  by  advertisers. 

Mr.  Casern's  point  is  well  taken.  Picture 
broadcasting  must  adhere  to  the  highest  stand- 


ards of  education  and  entertainment,  if  it  is  to 
be  popularized.  We  have  interviewed  many 
broadcasting  station  managements  on  this  sub- 
ject, and  have  found  that  this  fact  is  generally 
appreciated.  Program  managers  have  apparently 
learned  that  the  first  and  most  important  factor 
to  be  considered  in  any  radio  presentation  is  that 
it  shall  please  the  radio  audience.  To  this  rule, 
picture  broadcasting  is  no  exception. 

ANNUAL    REPORT    OF    THE     R.    C.    A. 

TpHE1  annual  report  of  the  Directors  of  the 
*  Radio  Corporation  of  America  to  stock- 
holders, for  1927,  indicates  a  substantial  im- 
provement in  the  corporation's  financial  position. 
The  net  income  transferred  to  surplus  amounts 
to  §8,478,320,  as  compared  with  $4,661,397  for 
the  previous  year.  About  seven  per  cent,  of  its 
gross  business  is  the  result  of  its  transoceanic 
services,  the  need  for  which  inspired  certain  naval 
officials  to  encourage  the  company's  original 
formation.  Its  combined  transoceanic  and  marine 
business  is  but  nine  per  cent,  of  its  total  business. 
It  collected,  during  1927,  $3,310,722  for  royal- 
ties, of  which  about  one  and  a  third  million  cover 
past  damages.  An  interesting  item  among  its 
assets  is  nearly  ten  and  a  half  million  dollars  in 
accounts  receivable.  It  is  not  generally  considered 
that  this  is  largely  inventory  and  it  may  be 
mostly  uncollected  royalties.  Although  more 
than  three  million  dollars  were  collected  as 
patent  royalties,  a  good  part  of  the  surplus  has 
been  devoted  to  reducing  the  value  of  the  patents 
credited  in  the  balance  sheet.  They  are  now  down 
to  a  little  over  five  and  a  half  million. 

THOSE  interested  in  studying  sales  and  dis- 
tribution figures  will  find  the  report  com- 
piled by  the  Electrical  Equipment  Division  of 
the  Bureau  of  Foreign  and  Domestic  Commerce, 
aided  by  N.  E.  M.  A.,  on  stocks  of  radio  equip- 
ment in  the  hands  of  radio  dealers,  very  illumi- 
nating. This  is  the  second  of  a  series  of  quarterly 
reports  to  be  issued.  A  little  over  30,000  dealers 
contributed  to  the  information.  On  October  t, 
the  dealers  had  65.921  battery  sets  in  stock  and, 


THE   KORN  SYSTEM  OF  RADIO  PICTURE  TRANSMISSION 

Doctor  Korn  (extreme  right)  demonstrating  his  latest  transmitter  to  German  police  officials.  Syn- 
chronism is  achieved  by  synchronous  motors  and  the  received  picture  is  made  on  light-sensitized  paper 
revolving  on  a  drum  in  a  light-proof  chamber.  It  is  said  that  the  armies  of  Italy  and  Japan  use  the 
Korn  "telautograph"  which  enables  aeroplane  observers  to  draw  simple  maps  and  then  radio  them 

direct  to  their  bases 


12 


RADIO  BROADCAST 


MAY,  1928 


on  January  i,  the  number  had  fallen  to  62,778. 
The  total  stock  on  hand  averages  but  two  per 
dealer,  a  number  insufficient  to  cause  uneasiness. 


Here  and  There 


THE  Association  of  National  Advertisers 
has  appointed  a  committee  to  make  a  survey 
of  broadcasting  as  an  advertising  medium.  They 
will  endeavor  to  ascertain  the  average  audience 
listening  to  a  radio  program.  Their  task  is 
equivalent  to  determining  the  number  of  crickets. 
chirping  at  any  given  instant,  in  a  swamp,  on  a 
foggy  summer  evening. 

LIEUTENANT  Commander  Craven  has  been 
assigned  to  the  Federal  Radio  Commission 
by  the  Navy  Department  to  grapple  with  the 
short-wave  problem. 

ALTHOUGH  it  is  definitely  known  that 
both  the  N.  B.  C.  and  the  Columbia  chains 
will  have  microphones  at  the  political  conven- 
tions, just  how  these  events  will  be  handled  is 
not  yet  made  clear.  Both  chains  have  commit- 
ments to  commercial  broadcasters  and  any  alter- 
ations to  their  schedules  are  made  at  the  price  of 
commercial  income.  Mr.  Aylesworth  of  the 
N.  B.  C.  has  pointed  out  these  difficulties  and 
issued  a  general  hint  through  the  press  that  the 
entire  convention  proceedings  might  be  spon- 
sored by  one  commercial  broadcaster.  It  appears 
that  there  was  no  great  rush  of  volunteers  as  a 
result. 

STATION  WOAI,  San  Antonio,  Texas,  re- 
cently joined  the  N.  B.  C.  network.  It 
had  been  one  of  the  few  independent  stations 
assigned  a  cleared  channel  by  the  Federal  Radio 
Commission.  The  Commission  has  no  control 
over  the  programs  radiated  by  a  station  and  is 


not  in  a  position  to  require  that  an  independent, 
assigned  to  a  cleared  channel,  shall  not  use  chain 
programs  after  receiving  such  an  assignment. 

ASST.  Secretary  of  Commerce  for  Aeronautics 
William  C.  McCracken,  Jr.,  announced 
that. approval  had  been  obtained  for  the  erection 
of  a  radio  control  station  at  Key  West  to  be 
operated  by  the  Airways  Division  of  the  Light- 
house Service.  It  will  provide  and  exchange 
weather  information  between  terminal  airports, 
radio  communication  to  aircraft  in  flight,  and  a 
radio  direction  service. 

THE  transatlantic  telephone  service  has  been 
subjected  to  a  forty  per  cent,  cut  in  rates, 
reducing  the  basic  rate  from  New  York  to  Lon- 
don to  $45  for  three  minutes  and  $15  for  each 
succeeding  minute.  The  hours  of  service  have 
been  extended  to  from  7:30  A.  M.  to  8  P.  M. 
Eastern  Standard  Time,  corresponding  to  12:30 
p.  M.  to  I  A.  M.  in  Great  Britain.  The  service  to 
Berlin,  Hamburg,  and  Frankfort  was  inaugurated 
on  February  10,  and  to  Sweden  on  the  2oth. 

THE  Department  of  Agriculture  is  extending 
its  broadcasting  service  through  NAA, 
Arlington,  by  issuing  weather  reports  on  several 
frequencies,  both  in  telegraph  and  voice.  The 
new  schedule  will  benefit  aviation  and  agricul- 
ture in  particular. 

OFFICIAL  reports  of  American  exports  of 
radio  apparatus  in  November  indicate 
their  aggregate  value  to  be  about  one  and  a 
quarter  million  dollars,  with  Canada,  Argentine, 
Australia,  and  Uruguay  the  largest  purchasers, 
f  f  f  A  CHINESE  broadcasting  organiza- 
tion has  been  formed  which  will  rent  time  from 
a  radio  telephone  plant  at  Shanghai.  A  subscrip- 
tion of  ten  dollars  a  year  is  to  be  charged  each 


Estimated  Number  of  Radio  Receivers  in  Use 

United  States,  January  1,  1928 

'"pH  ROUGH  the  courtesy  of  the  radio  division,  National  Electrical  Manufacturers' 

A  Association,  the  figures  showing  the  number  of  radio  sets  now  in  use  are  presented. 

New  York,  California,  and  Illinois,  are  the  leaders  in  order,  according  to  this  survey. 

Note  the  number  of  estimated  sets  in  the  southern  states,  figures  which  are  interesting, 

in  view  of  the  efforts  of  some  Congressmen,  especially  from  southern  states,  to  have  an 

"equitable  station-power  distribution"  clause  made  a  part  of  the  present  radio  act. 


STATE 

Alabama. 

Arizona  .... 

Arkansas 

California     . 

Colorado 

Connecticut 

Delaware 

District  of  Columbia 

Florida 

Georgia  .... 

Idaho      .... 

Illinois    .... 

Indiana  .... 

Iowa       .... 

Kansas 

Kentucky 

Louisiana 

Maine     .... 

Maryland 

Massachusetts  . 

Michigan 

Minnesota    . 

Mississippi   . 

Missouri 

Montana 


TOTAL  SETS 
45,000 

25,000 

42,000 

704,000 

89,000 

125.000 

15,000 

44,000 

73,000 

64,000 

26.000 

539.000 

184,000 

176,000 

104,000 

46,000 

74,000 

39,000 

56,000 

328,000 

336.000 

129,000 

28,000 

227,000 

29,000 


STATE 

Nebraska 
Nevada  . 
New  Hampshire 
New  Jersey  . 
New  Mexico 
New  York    . 
North  Carolina 
North  Dakota   . 
Ohio  .... 
Oklahoma     . 
Oregon    . 
Pennsylvania 
Rhode  Island     . 
South  Carolina  . 
South  Dakota 
Tennessee     . 
Texas      .      .      . 
Utah       .      .     . 
Vermont . 
Virginia 
Washington 
West  Virginia    . 
Wisconsin     . 
Wyoming 
TOTAL 


TOTAL  SETS 

118,000 

15,000 

25,000 

209,000 

18.000 

876.000 

48.000 

35,000 

464,000 

104,000 

121,000 

501.000 

53,000 

22,000 

41,000 

52,000 

188,000 

33,000 

19,000 

56,000 

217.000 

50,000 

169,000 

20.000 

7,000,000 


member  to  meet  the  cost  of  providing  programs 
and  employing  announcers,  Iff  THE 
MUNICIPAL  authorities  of  Buenos  Aires  are  plan- 
ning to  extend  the  service  of  their  station,  LOS, 
in  the  Colon  Theatre,  which  has  so  far  been  used 
exclusively  for  broadcasting  operas  and  concerts 
from  the  stage  of  the  theatre,  f  \  |  THE 
NUMBER,  of  licenses  in  the  Australian  broadcast- 
ing system  has  now  reached  300,000.  One  high- 
power  station  has  been  erected  in  each  capital 
city,  and  in  Melbourne  and  Sidney  there  are 
two.  Telephone  lines  for  interchange  of  programs 
are  frequently  used.  I  f  f  A  CONTRO- 
VERSY rages  as  to  radio  concessions  extended 
by  various  Chinese  administrations.  Japan  has 
an  agreement,  negotiated  by  the  Chinese  Minis- 
try of  the  Navy,  which  gives  it  a  monopoly  for 
thirty  years.  In  1921,  the  Federal  Telegraph 
Company  made  a  contract  with  the  Chinese 
Ministry  of  Communications  for  five  stations  to 
be  operated  by  the  American  company  for 
twenty  years.  The  British  also  obtained  con- 
tracts on  behalf  of  the  Marconi  Wireless  Tele- 
graph Company.  Apparently  an  exclusive  license 
in  China  is  non-exclusive.  J  f  I  IN 
EUROPE,  the  International  Radiophone  Union 
regulates  the  frequencies  and  time  assignments 
of  broadcasting  stations.  The  Hungarian  Govern- 
ment has  been  barred  from  admission  to  this 
organization  at  the  plea  of  Czecho-SIovakian 
delegates.  The  Hungarians  have  been  accused 
of  using  their  stations  to  spread  propaganda,  at- 
tacking the  Treaty  of  Trianon,  thereby,  en- 
dangering the  integrity  of  Czecho-SIovakia. 
I  f  I  ALL  EXISTING  telegraph  records 
were  broken  during  the  Christmas  season  in 
England  when  the  inter-empire  beam  radio 
telegraph  system  transmitted  no  less  than  31,694 
Christmas  greetings  from  Great  Britain  to  the 
dominions  at  a  speed  of  400  words  per  minute, 
withoutasinglerepetitionbeingrequired.  ?  I  t 
GERMAN  POLICE  systems  have  adopted  the  Korn 
system  of  picture  transmission  which  is  built 
along  lines  which  have  become  conventional. 
Korn  is  a  pioneer  in  the  field,  having,  as  early  as 
1907,  transmitted  newspaper  photographs  be- 
tween Paris  and  London.  Synchronous  motors 
and  neon  lights  are  used. 

THE  PATENT  SITUATION 

IN  A  decision  released  February  18,  the  Dis- 
trict Court  for  Delaware  held  that  Clause  IX 
of  the  Radio  Corporation  of  America  license 
agreement  with  radio  set  manufacturers  con- 
stituted an  unfair  method  of  competition  in 
violation  of  the  Clayton  Act.  Clause  IX  of  the 
license  agreement  required  that  each  set  made 
under  license  be  equipped  with  a  complete  com- 
plement of  R.  C.  A.  tubes,  sufficient  to  make 
them  initially  operative.  A  suit  for  $10,000,000 
damages  was  subsequently  brought  by  a  group 
of  independent  tube  manufacturers  who  avowed 
that  the  operation  of  this  clause  virtually 
paralyzed  their  business.  Section  III  of  the 
Clayton  Act  specifically  provides  that  its  pro- 
visions shall  apply  whether  the  article,  in  behalf 
of  which  unfair  methods  are  employed,  is  pat- 
ented or  not. 

In  a  suit  brought  by  the  Westinghouse  Com- 
pany, under  the  Armstrong  patent,  against  the 
Tri-City  Radio  Company,  the  effect  of  continued 
acquiescence  and  acceptance  of  royalties  on  cer- 
tain regenerative  sets  sold  prevented  the  collec- 
tion of  damages.  The  Tri-City  was.  a  licensee 
under  the  Armstrong  patent  prior  to  its  acquisi- 
tion by  the  Westinghouse  Company.  It  ap- 
pointed a  sub-manufacturer  to  make  the  goods 
for  it,  although  the  original  license  did  not  per- 
mit such  sub-manufacture 

—  E.  H.  F. 


A  SHORT-WAVE  RECEIVER  FOR  ii.i  TO  119  METERS 


THIS  article  describes  the  construction  of  a 
single-tube  receiver  and  coils  to  go  with  it 
to  cover  the  frequency  band  between  1 .37 
and  26.7  megacycles  ( 1 1 .2  to  2 1 9  meters  approxi- 
mately) .The  receiver  may  be  used  with  any  audio 
amplifier  system. 

It  is  completely  shielded  in  a  copper  box  ioj' 
wide,  9!"  deep,  and  6"  high.  The  copper  sheet 
from  which  the  box  is  made  is  h"  thick.  All 
joints  are  soldered  and  the  top  opening  of  the 
box  is  reenforced  with  \"  by  \"  by  ,',,"  angle 
brass  which  is  soldered  to  the  copper.  Holes  are 
drilled  in  the  angle  brass  for  \"  8-32  machine 
screws  with  which  to  fasten  on  the  cover.  The 
screws  are  soldered  into  the  angle  brass.  The 
cover  is  of  sheet  copper  reenforced  at  the  edges 
and  center  with  a  strip  of  brass  i"  wide  by  TV' 
thick.  Holes  are  drilled  in  the  strip  around  the 
edge  of  the  cover  to  allow  the  cover  to  fit  down 
on  the  angle  brass  where  it  is  tightly  held  by 
hexagonal  nuts.  Although  it  takes  a  few  moments 
to  remove  and  replace  the  cover  when  changing 
coils,  this  method  of  shielding  has  been  found 
to  be  very  complete  and  mechanically  strong. 

The  copper  box  is  screwed  to  a  10"  by  1 1 J"  by 
A"  wood  baseboard  to  which  is  also  fastened  by 
three  wood  screws  the  7"  by  12"  bakelite  panel. 
The  only  objects  on  the  panel  are  the  tuning 
agd  regeneration  controls  and  the  output  bind- 
ing posts.  Note  that  the  copper  box  is  not  cen- 
tered behind  the  baseboard  but  is  set  in  \"  from 
the  left-hand  edge  of  the  panel  in  order  to  allow 
room  for  the  output  binding  posts  at  the  right. 
At  the  rear  of  the  set  there  is  a  bakelite  strip 
on  which  are  mounted  four  binding  posts  for  con- 
nections to  the  antenna,  A  battery,  and  to  the  de- 
tector positive  terminal  of  the  B  battery.  The 
three  battery  wires  go  into  the  copper  box 
through  one  hole  and  the  antenna  lead  through 
another.  Most  of  the  parts  are  mounted  on  an 
inside  baseboard  loj",  by  8^",  by  A"  thick. 

As  will  be  seen  by  reference  to  Fig.  I,  the  an- 
tenna is  coupled  to  the  antenna  coil  through  a 
General  Radio  midget  variable  condenser  of 
15-mmfd.  capacity,  C,.  A  General  Radio  coil 
mounting  holds  the  plug-in  coils  and  is  spaced 
a  generous  distance  from  the  sides  of  the  box. 
The  tuning  condenser,  C3,  is  a  Cardwell  of  50- 


By  Lloyd  T.  Goldsmith 

Col.  E.  H.  Green  Radio  Rnrarch 


A  "Super"  for  Code  Work 

THE  short-wave  receiver  described  in  this  article 
has  been  designed  for  use  with  any  ordinary 
audio  amplifier,  and  when  so  used,  will  be  found 
extremely  sensitive,  especially  for  code  reception. 
The  main  purpose  for  its  design,  however,  is  its 
adaptation  to  the  super-heterodyne  unit  described 
on  the  pages  following  those  devoted  to  the  present 
article.  The  super-heterodyne  combination  will 
not  be  satisfactory  for  short-wave  phone  reception 
due  to  the  peaked  characteristics  of  the  intermediate- 
frequency  amplifier.  It  will,  on  the  other  hand,  be 
wonderfully  sensitive  for  code  reception. 

— THE  EDITOR. 


7Ant. 


mmfd.  capacity  of  the  straight  frequency-line 
type.  The  regeneration  condenser,  C2,  is  a  Na- 
tional of  250-mmfd.  capacity.  The  latter  two 
condensers  are  mounted  directly  on  the  copper 
box  and  bakelite  panel.  Each  is  provided  with  a 
4"  National  Velvet  vernier  dial. 

The  grid  condenser,  C4,  is  a  loo-mmfd.  San- 
gamo  across  which  is  a  Tobe  8-megohm  grid 
leak,  Ri.  The  detector  tube  is  a  UX-2OI-A  and 
fits  in  a  General  Radio  ux  type  socket  mounted 
on  a  General  Radio  rubber  cushion  to  absorb 
shocks  and  reduce  noises.  The  leads  to  the  socket 
are  of  flexible  rubber-covered  wire.  The  radio- 
frequency  plate  choke,  U,  is  a  Samson  No.  85 
of  85  tnh.  inductance  The  audio-frequency 
choke,  U,  in  the  positive  B-battery  lead  is  a 
Samson  No.  }  of  3  henrys  inductance.  The  audio- 


~l 


- I 


A 

FIG.    I 
Circuit  diagram  of  the  short-wave  receiver  described  in  this  article 

13 


14 


RADIO  BROADCAST 


MAY,  1928 


frequency  current  is  bypassed  to  filament  through 
a  i-mfd.  Tobe  condenser,  C6,  which  in  the 
photograph  can  be  seen  mounted  on  the  base- 
board beneath  the  regeneration  condenser.  The 
copper  box  is  grounded  to  the  positive  A  binding 
post. 

No  rheostat,  filament  switch,  or  voltmeter  is 
provided  on  the  receiver  because  it  is  designed 
primarily  to  be  used  with  the  screen-grid  tube 
super-heterodyne  described  in  the  article  follow- 
ing this  one  in  this  same  issue,  and  common  A 
and  B  batteries  are  used,  the  A  battery  connec- 
tions for  the  receiver  being  taken  off  the  filament 
terminals  of  the  second  detector  socket  of  the  su- 
perheterodyne. In  this  way  the  filament  switch 
on  the  super-heterodyne  controls  the  filaments  of 
all  the  tubes,  and  the  voltmeter  reads  their  fila- 
ment voltage,  which  is  adjusted  by  the  master 
rheostat. 

The  plug-in  coils  are  mounted  between  J" 
bakelite  strips  provided  with  General  Radio  type 
274-1'  plugs.  The  socket,  or  base,  into  which  the 
coils  are  inserted,  is  a  General 
Radio  274-8  base,  which  retails 
complete  for  $t.oo.  The  plugs  on  the 
coils  must  be  so  spaced  that  they 
will  plug  into  this  standard  base. 
The  tickler  is  mounted  next  to  the 
antenna  coil  when  it  is  of  the  same 
diameter  as  the  latter,  but  in  the 
larger  coils,  to  save  space,  it  is 
mounted  within  the  secondary  coil. 
In  any  case,  the  tickler  should  be  at 
the  filament  end  of  the  secondary 
coil. 

The  coils  are  wound  on  a  bakelite 
tube  which  has  been  cut  in  half 
diametrically  and  held  together  by 


SKCLONDARY  (.on. 

1  K.KM-R    (]oil. 

HASPS 

No.  of 
7'urnj 

Diameter 
(Inches) 

.Site  of 
Wire 
(D.C.C.) 

No.  of 
7  urns 

Diamflfr 

(In,  /'fit 

Site  of 
Wire 
(D.C.C.) 

I'Tfquerttv 
(Megacycles) 

Wavelenftb 
(Meiers- 

dppTOX.^ 

4 

18 

1 

I 

16.7  -26.7 

.8      -11.2 

7 

18 

4 

11.5  -18 

26.  1-16.7 

i  i 

18 

6 

8.3  -13.3 

36.2-22.6 

t» 

18 

10 

i 

6.     -  9.4 

50     -31.9 

U 
23 

\ 

18 

)  } 
16 

4.2  -  6.52 
2.87-  4.6 

71.4-46 
104.5-65.2 

}7 

18 

10 

1 

2.1    -    3.33 

143    -go 

54 

, 

22 

! 

2 

'    IT     i    '~ 

219   -138 

A    TABLE    OF    COIL    SIZES 


-Bakelite  Tubing 
'  Brass  end  Ring 


HG.    2 
Constructional  deta  Is  for  the  coil  form 


C1 


L3 


L4 


Comp  ete  details  of  the  number  of  turns  for  the  secondary  coil,  Li,  and 
the  tickler  coil,  l.:,  for  various  frequencies  are  incorporated  in  this  table 


Brass  Ring  drilled  &  tapped 

Machine  Screw  brass  end  rings.  Kig.  2  shows  the  con- 

struction of  the  coil  form.  The  desired 
number  of  turns  is  wound  on  the  form 
and  given  two  light  coats  of  collodion. 
When  the  coil  is  dry  the  screws  are 
removed  from  the  end  rings,  the  latter 
are  slipped  out,  and  the  bakelite 
form  is  pushed  together  so  that  the 
coil  can  be  slipped  off.  The  inside  of 
the  coil  is  then  given  a  coat  of 
collodion  to  add  to  its  mechanical 
strength. 

The  accompanying  table  gives  data 
on  the  number  of  turns,  size  of  wire, 
diameter    of   the   coil,   and    the   fre- 
quency band  covered  with  the  tuning 
condenser  used.  In  the  front  view  of  the  receiver 
are  shown  the  1  75-meter  coil,  the  8o-meter  coil, 
and  the  2o-meter  coil,  while  the  interior  view  of 
the  set  shows  the  40-meter  coil  in  place. 

Elaborate  constructional  details  have  not  been 
given  in  this  article  for  it  is  felt  that  those  in- 
terested will  be  sufficiently  versed  in  the  art  of 
amateur  set  construction  to  build  the  receiver 
from  those  data  presented.  The  layout  of  appara- 
tus can  be  distinctly  followed  by  reference  to 
the  photographs,  and  the  circuit  diagram  is 
so  simple  as  not  to  require  an  elaborate  ex- 
planation. 

The  receiver  as  described  is  complete  and 
ready  for  operation  with  any  audio  amplifier. 
It  was  primarily  designed,  however,  for  code  re- 
ception, and  particularly  to  be  used  in  conjunc- 
tion with  the  super-heterodyne  unit  described  in 
the  article  beginning  on  the  next  page. 

I  he  following  parts  are  required  for  the  single- 
tube  receiver  described: 


AN    INTERIOR    VIEW    OF    THE    RECEIVER 

The  parts  are  numbered  for  cross  reference  to  the  list  of  parts  in  the  column  immediately  to  the  right 


LIST  OF   PARTS 

Ci  —  General   Radio  ij-Mmfd.  Midget  Variable 

Condenser 

Cj  —  Cardwell  jo-Mmfd.  Variable  Condenser 
Q  —  National  25O-Mmfd.  Variable  Condenser 
Q  —  Sangamo  [oo-Mmfd.  Fixed  Condenser 
Ci  —  Tobe  i-Mfd.  Fixed  Condenser 
RI  —  Tobe  8-Megohm  Grid  Leak 
LI,  L2  —  Plug-in  Coils  (Specifications  in  Text) 
L3  —  Samson  No.  85  Choke 
L«  —  Samson  No.  3  Choke 
General  Radio  ux  Tube  Socket 
Six  Eby  Engraved  Binding  Posts 
General  Radio  No.  274-8  Coil  Mount 
General  Radio  Rubber  Socket  Cushion 
Two  4"  National  Velvet  Vernier  Dials 
7"  x  12"  x  ,Y'  Bakelite  Panel 
10"  x  1  1  5"  x  |'e"  Wood  Baseboard 
io\"  x  8£"  x  T6e"  Wood  Baseboard 
a1/'  Copper  Box  with  Cover  lof  "  x  gj"  x  6" 
Brass  Angle,  Brass  Strip,  Angles,  etc. 


TWO  SCREEN-GRID  TUBES  ARE  USED  IN  THE  INTERMEDIATE  AMPLIFIER  OF  THIS  SUPER-HETERODYNE  UNIT 
The  unit  has  been  devised  for  use  with  an  existing  short-wave  receiver  (such  as  that  described  in  the  previous 
article),  converting  it  into  a  remarkably  efficient  short-wave  super-heterodyne,  especially  suited  for  code  signals 

A  Superheterodyne  for  Short- Wave  Code  Signals 

By  Lloyd  T.  Goldsmith 


THE  standard  receiver  used  for  short-wave 
code  reception  usually  consists  of  a  detector 
(such  as  that  described  in  the  preceding 
two  pages)  and  one  stage  of  audio-frequency  am- 
plification, although  sometimes  a  second  audio 
stage  is  used  in  an  effort  to  secure  more  volume. 
In  the  latter  case,  unless  a  selective  amplifier  is 
used,  the  noise  level  is  amplified  in  about  the 
same  proportion  as  the  received  signal,  which  is 
undesirable,  as  the  real  aim  is  to  amplify  the 
signal  and  not  the  noise.  This  difficulty  suggests 
that  the  signal  be  amplified  at  a  radio  frequency 
rather  than  at  an  audio  frequency  in  an  effort 
to  amplify  it  more  than  the  noise  background. 
Radio-frequency  amplification  at  very  high  radio 
frequencies  has  not  been  found  very  satisfactory 
but  if  the  signal  be  changed  to  a  radio  frequency 
of  the  order  of  20  to  100  kilocycles,  amplification 
is  not  only  satisfactory  for  the  signal  gain  alone 
but  from  the  point  of  view  of  increasing  the  signal- 
to-noise  ratio.  T  his  is  what  is  done  in  the  super- 
heterodyne. In  addition,  if  the  radio-frequency 
amplifier  stages  are  sharply  tuned,  the  selectivity 
of  the  receiving  apparatus  as  a  whole  is  very  ma- 
terially increased. 

With  the  increase  in  the  number  of  trans- 
mitting stations  operating  on  the  shorter  waves 
the  need  is  becoming  greater  for  a  receiver  giving 
all  possible  practical  selectivity.  In  an  attempt 
to  realize  these  requirements  the  super-hetero- 
dyne described  in  this  article  was  built. 

Super-heterodyne  receivers  using  2OI-A  type 
tubes  with  impedance-coupled  and  tuned  trans- 
former-coupled intermediate-frequency  ampli- 
fiers built  and  tested  at  the  Massachusetts  Insti- 
tute of  Technology  have  been  found  very  much 
worth  while  in  the  reception  of  long-distance 
short-wave  telegraph  signals.  Upon  obtaining  the 
new  screen-grid  tubes,  a  super-heterodyne  was 
constructed  at  the  Institute  using  these  tubes 
as  the  intermediate-frequency  amplifiers.  The 
construction  of  this  receiver  is  described  here. 


The  arrangement,  as  will  be  seen  by  referring 
to  Fig.  i,  consists  of  two  stages  of  intermediate- 
frequency  amplification  using  screen-grid  tubes, 
a  beat  frequency  oscillator,  a  detector,  and 
one  stage  of  audio  amplification,  using  ZOI-A 
tubes.  The  unit  as  a  whole  is  intended  to  follow 
any  short-wave  receiver,  using  the  latter's  de- 
tector tube  as  an  autodyne  frequency  converter, 
and  changing  the  signal  frequency  to  50  kilo- 
cycles. The  super-heterodyne  unit  is  particularly 
adaptable  to  the. short-wave  circuit  described  on 
the  previous  two  pages. 

The  first  intermediate-frequency  stage  has  a 
tuned  transformer  input  circuit.  The  trans- 
former, T,  has  an  air  core  and  is  a  spool  made  of 
\"  diameter  bakelite  having  a  winding  space 
-J"  wide  by  j"  deep.  The  secondary  winding  con- 
sists of  1000  turns  of  No.  28  d.c.c.  wire.  Over  this 
are  placed  a  few  layers  of  paper  to  prevent  pos- 
sible grounding  of  the  two  windings.  Over  the 
paper  the  primary  is  placed,  consisting  of  250 
turns  of  the  same  wire.  The  secondary  can  be 
tuned  to  an  intermediate  frequency  of  50  kilo- 
cycles by  means  of  a  5OO-mmfd.  variable  con- 
denser or  to  30  kilocycle?  if  an  additional  fixed 
capacity  of  1000  mmfd.  is  shunted  across  the 
variable  condenser. 

\\ith  a  given  plate  voltage  the  voltage  ampli- 
fication of  the  screen-grid  tube  is  directly  pro- 
portional to  the  effective  impedance  which  can 
be  built  up  in  its  plate  circuit.  (See  "Characteris- 
tics of  shielded-grid  Pliotrons,"  by  A.  W.  Hull 
and  N.  H.  Williams,  and  "Measurements  of  High- 
l-requency  Amplification  with  Shielded-lirid 
Pliotrons,"  by  A.  W.  Hull.  Both  of  these  papers 
appeared  in  the  Physical  Review,  April,  10,26, 
Vol.  27.)  this  fact  should  be  kept  in  mind  when 
choosing  values  of  inductance  and  capacitance 
to  be  used  as  a  coupling  impedance.  In  this  case 
the  coils,  L,  are  No.  85  Samson  choke  coils  which 
can  be  tuned  from  20  to  50  kilocycles  by  a  500- 
mmfd.  variable  condenser.  Honeycomb  coils 

15 


were  tried  as  coupling  impedances  and  slightly 
greater  amplification  was  obtained,  but  because 
of  the  ease  of  mounting  and  compactness  of  the 
Samson  choke  coils,  they  were  used  in  the  final 
receiver.  These  chokes  are  helical  wound  and 
although  their  direct-current  resistance  is  higher 
than  that  of  a  honeycomb  coil  having  the  same 
inductance,  their  effective  resistance  at  radio 
frequencies  is  much  less. 

The  variable  condensers  are  provided  with 
insulating  shafts  to  keep  the  .radio-frequency 
circuits  as  far  away  from  the  panel  as  possible 
and  all  except  the  first  are  mounted  on  the  shields 
with  insulating  pillars.  The  interstage  coupling 
condensers,  Q,  are  of  2ooo-mmfd.  capacity  and 
the  grid  leak,  Ri,  is  of  100,000  ohms.  The  B- 
battery  voltage  is  135  volts  and  the  screen-grid 
voltage  is  67.5  volts. 

The  filament  voltage  is  reduced  to  5  volts  by 
means  of  a  2-ohm  master  rheostat  in  the  positive 
A-battery  lead  and  the  filament  voltage  of  the 
screen-grid  tube  is  further  reduced  to  3.3  volts  by 
15-ohm  fixed  resistances,  R,  placed  in  each  of 
their  negative  filament  leads.  The  grid  returns 
are  brought  to  the  battery  sides  of  these  resist- 
ances giving  a  grid  bias,  equal  to  the  drop  in  the 
resistance  R,  of  approximately  i  .7  volts  negative. 

For  grid  detection  in  the  second  detector  the 
grid  condenser  is  of  2ooo-mmfd.  capacity  and  the 
leak  can  be  from  4  to  8  megohms  where  the  plate 
voltage  is  45  volts.  Provision  is  made  for  a  C 
battery  if  plate  detection  is  used. 

A  small  amount  of  regeneration  or  resistance 
neutralization  is  introduced  into  the  plate  cou- 
pling impedance  of  the  second  intermediate- 
frequency  stage  to  secure  increased  amplification 
in  that  stage.  The  effective  shunt  impedance  of 
the  parallel  circuit,  consisting  of  the  plate  coil 
and  condenser,  is  limited  by  the  resistance  of 
the  circuit.  The  introduction  of  regeneration  re- 
duces this  effective  resistance,  giving  a  greater 
effective  impedance  in  the  plate  circuit,  with 


16 


RADIO  BROADCAST 


MAY,  1928 


correspondingly  increased  amplification.  (See 
"Complete  Suppression  of  a  Single  Frequency 
by  Means  of  Resonant  Circuits  and  Regenera- 
tion," by  J.  A.  Stratton.  Journal  Optical  Society 
of  America.  Vol.  13,  No.  i,  July  1926.)  Regenera- 
tion is  accomplished  by  means  of  a  small  tickler, 
L2,  in  the  detector  plate  circuit  of  25  turns  wound 
directly  on  the  plate  coil  of  the  second  inter- 
mediate-frequency stage.  The  tickler  can  be  cut 
in  or  out  as  desired  by  means  of  a  switch,  K, 
mounted  on  the  front  panel.  The  receiver  was 
not  designed  for  broadcast  reception  and  with 
air  condensers  to  tune  the  intermediate-fre- 
quency stages,  the  tuning  is  too  sharp  for  quality 
reception.  If,  however,  fixed  condensers  of  the 
proper  capacity  are  used  to  tune  the  intermediate 
stages,  it  is  probable  that  the  response  curve 
would  include  a  band  10  kc.  wide.  The  amplifi- 
cation would  probably  be  reduced  accordingly. 
With  a  5O-mmfd.  tuning  condenser  across  the 
secondary  of  the  short-wave  detector  out  of 


voltage  is  then  necessary  as  when  receiving 
unmodulated  signals. 

The  oscillator  is  a  "shunt  feed"  Hartley  type 
the  frequency  of  which  is  regulated  by  a  variable 
condenser  of  joo-mmfd.  capacity  in  shunt  with  a 
fixed  condenser,  Cz,  of  looo-mmfd.  capacity  for 
3o-kilocycle  operation,  or  yjo-mmfd.  capacity  for 
5O-kiIocycle  operation.  The  oscillator  coil,  LS, 
consists  of  I  500  turns  of  No.  28  wire  wound  on 
the  same  kind  of  spool  as  is  used  for  the  input 
transformer,  T,  the  filament  tap  being  made  one 
third  of  the  way  from  the  grid  end  of  the  coil. 

Some  difficulties  were  encountered  in  adding 
a  stage  of  audio-frequency  amplification  as  the 
separation  between  a  5O-kilocycle  radio-fre- 
quency signal  and  an  audio-frequency  signal  of 
approximately  2  kilocycles  is  relatively  small. 
To  keep  the  jo-kc.  component  out  of  the  audio- 
frequency circuit  a  single-section  filter  having 
a  cut-off  at  approximately  5  kc.  is  used  in  the 
detector  plate  circuit  of  the  detector.  The  filter  is 


stage  coupling  through  the  B-battery  leads.  All 
battery  binding  posts,  as  well  as  the  output 
posts,  are  mounted  on  a  bakelite  terminal  strip 
at  the  rear  of  the  set. 

The  aluminum  shields  are  5"  by  6"  by  9" 
except  the  first  which  was  cut  down  to  4"  by 
6"  by  9".  The  first  shield  contains  the  input 
transformer,  with  its  secondary  fixed,  and  varia- 
ble condensers.  The  second  and  third  shields 
contain  the  first  and  second  stages  of  inter- 
mediate-frequency respectively,  along  with  their 
associated  coils,  condensers,  etc.  The  ij-ohm 
fixed  resistance  in  the  filament  circuit  of  the  first 
screen-grid  tube  is  within  its  aluminum  shield 
while  the  fixed  resistance  in  the  filament  circuit 
of  the  second  screen-grid  tube  is  mounted  at  the 
rear  of  the  baseboard  behind  the  shields. 

The  input  lead  to  the  first  stage  is  brought  out 
through  the  top  of  the  first  shield  and  connects 
directly  to  the  control  grid  cap  of  the  first  screen- 
grid  tube,  which  projects  through  a  hole  in  the 


r 


Output 


._v_ 


FIG.     I 

The  circuit  arrangement  of  the  short-wave  super-heterodyne  unit.  The  out- 
put of  the  short-wave  receiver  which  precedes  the  "super"  connects  to  the 
two  input  posts  on  the  extreme  left.  The  first  two  tubes  are  the  intermediate 
amplifiers,  and  they  are  followed  by  the  second  detector  and  audio  stage. 
The  lower  tube  is  the  beat  frequency  oscillator 


which  this  amplifier  works,  the  outfit  is  as  selec- 
tive as  one  dares  make  it.  An  a.c.  note  appears 
and  disappears  in  one  half  a  division  on  the 
100  division  scale  of  the  condenser  when 
working  in  the  3-  to  4-megacycle  (75-100 
meter)  band. 

In  the  ordinary  short-wave  receiver  employing 
a  simple  oscillating  tube  as  a  detector  of  c.w. 
signals,  the  detector  is  made  to  oscillate  at  a 
frequency  differing  one  or  two  kilocycles  from 
the  incoming  signal  and  the  resulting  audible 
beat  is  heard  in  the  telephone  receivers.  In  tun- 
ing the  detector  when  followed  by  the  inter- 
mediate-frequency amplifier  described  here,  the 
beat  frequency  is  made  an  inaudible  frequency 
of  50  kilocycles,  instead  of  the  usual  one  or  two 
kilocycles.  To  reduce  this  to  an  audible  frequency 
an  oscillator  whose  frequency  can  be  varied  is 
made  to  beat  with  the  jo-kilocycle  intermediate 
frequency  and  give  a  difference  frequency  of  one 
or  two  kilocycles  as  desired.  The  beating  oscilla- 
tor voltage  is  fed  to  the  grid  circuit  of  the  second 
detector  tube  through  the  grid  leak  resistor.The 
audible  beat  frequency  produced  in  the  second 
detector  is  then  amplified  by  the  stage  of  audio 
amplification.  For  phone  reception  the  oscillator 
tube  is  removed  from  its  socket  as  no  beating 


a  simple  "pi"  section  consisting  of  a  3-henry 
choke  in  the  detector  plate  lead  preceded  and 
followed  by  2ooo-mmfd.  and  looo-mmfd.  fixed 
condensers  respectively.  The  choke  is  a  Samson 
No.  3  which  has  a  small  open  iron  core. 

There  is  nothing  unusual  about  the  stage  of 
audio  amplification.  The  transformer  is  a  Samson 
with  a  6  to  i  ratio  and  there  is  provided  a  pair  of 
output  binding  posts  as  well  as  the  usual  output 
jack.  The  B-battery  voltage  is  135  volts  and  the 
grid  battery  is  4.5  volts. 

The  baseboard  is  23j"by  io"by  j".  The  front 
panel  is  of  bakelite  and  is  24"  by  7"  by  •&". 
The  first  three  dials  tune  the  intermediate- 
frequency  stages  while  the  fourth  controls  the 
frequency  of  the  beating  oscillator.  All  the  dials 
are  4"  National  Velvet  Vernier  dials.  At  the  right 
there  is  provided  a  Weston  double-range  volt- 
meter to  read  plate  and  filament  voltages  while 
below  it  are  the  2-ohm  master  rheostat,  filament 
switch,  and  output  jack.  The  regeneration  switch 
is  between  the  third  and  fourth  dials  and  is  a 
Yaxley  jack  switch  of  the  single-pole  double- 
throw  type.  The  two  input  binding  posts  are  at 
the  extreme  left  of  the  panel.  Plate-voltage  leads 
are  provided  with  Samson  3-henry  chokes  and 
i-mfd.  bypass  condensers  to  prevent  inter- 


top  of  the  shield.  The  output  lead  of  the  first 
amplifier  stage  is  brought  out  through  a  hole  in 
the  top  of  the  second  shield  and  connects  with 
the  grid  cap  of  the  second  shield  grid  tube,  which 
projects  through  a  hole  in  the  third  shield.  To 
prevent  pick-up  by  these  leads  they  are  wrapped 
in  copper  foil  which  in  turn  is  grounded.  This 
aids  in  the  prevention  of  oscillation  in  the  stages 
and  helps  materially  in  securing  stable  operation. 
The  tube  sockets  are  raised  on  blocks  of  wood  in 
order  that  the  control  grid  may  project  as  far 
as  possible  through  the  hole  in  the  top  of  the 
shield.  The  grid  terminal  is  insulated  where  it  is 
likely  to  come  into  contact  with  the  edge  of  the 
hole  and  the  grid  lead  is  wound  into  a  spiral 
spring  which  makes  a  tight  connection  to  the 
grid  terminal. 

The  last  shield,  placed  at  right  angles  to  the 
first  three,  contains  the  audio  beating  oscillator. 
All  the  shields  are  connected  together  and 
brought  to  a  binding  post  at  the  rear  of  the  set 
marked  "Ground."  In  this  way  effects  of  ground- 
ing the  shields  individually  or  collectively,  the 
negative  A  alone,  or  shields  and  battery  together, 
may  be  noted.  Behind  the  oscillator  shield  there 
is  the  detector,  filter,  and  the  stage  of  audio  am- 
plification. 


MAY,  1928 


A  SUPER-HETERODYNE  FOR  SHORT-WAVE  CODE  SIGNALS 


17 


400 


350 


300 


o  250 


o 

c: 


200 


VOLTAGE  AMPLIFICATION 
SINGLE  STAGE  R.F.  AMP. 


A- Screen-Grid  Tube 
With  Regeneration 


B- Screen-Grid  Tube 
Without  Regeneration 


C-UX-201-A 

Transformer-Coupled 


D-UX-240 

Impedance-Coupled 


150 


100 


49  50  51 

FREQUENCY-KILOCYCLES 

FIG.    2 

Showing  the  voltage  amplification  for  a  single 
without  regeneration  and  for  different  tubes  and 

EXAMINING    THE    CURVES 

AN  EXAMINATION  of  the  amplification 
curves  of  Fig.  2  shows  that  at  50  kilocycles 
the  maximum  amplification  obtained  in  one  stage 
with  the  plate  impedance  used  is  155  without 
regeneration  and  370  with  regeneration.  By 
amplification  is  meant  the  ratio  of  the  voltage 
appearing  across  the  plate  impedance  to  the 
voltage  impressed  on  the  grid.  The  curves  also 
indicate  the  sharpness  of  tuning  of  a  single  stage. 
The  amplification  obtained  in  both  stages  of 
intermediate  frequency  is  rather  difficult  to 
measure  accurately  because  it  is  so  great  but  is 
in  the  order  of  25,000  with  regeneration.  The 
amplification  obtained  in  the  stages  of  inter- 
mediate frequency  of  other  super-heterodynes 
built  at  Massachusetts  Institute  of  Technology 
using  ux-2Oi-A  tubes  has  been  (see  Fig.  2)  in 
the  order  of  25  for  one  tuned  amplifier  stage  and 
16  for  one  stage  of  impedance-coupled  amplifica- 
tion with  high-mu  tubes.  (These  data  were 
presented  in  an  unpublished  report  of  Green 
Radio  Research,  Massachusetts  Institute  of 
Technology). 

A  compromise  had  to  be  made  between  greater 
amplification  secured  by  increased  regeneration, 
and  sharpness  of  tuning.  In  the  present  arrange- 
ment the  amplifier  is  not  well  adapted  to  the 
reception  of  voice  and  music  as  the  width  of  the 
band  of  frequencies  passed  in  a  single  stage  is 
not  more  than  1400  cycles. 

Too  much  stress  cannot  be  laid  upon  the  need 
of  proper  shielding  when  using  the  screen-grid 
tube.  The  grid  leads  from  the  tubes  must  be 
shielded  from  all  the  plate  circuit  apparatus  of 
the  same  tube.  The  covers  of  the  shields  would 
be  much  better  flanged  to  eliminate  cracks  after 
the  cover  is  put  on.  The  holes  for  the  wires 


should  be  as  few  as  pos- 
sible and  no  larger  than 
necessary  All  radio- 
frequency  circuits 
should  be  kept  within 
the  shields,  by  the  use  of 
chokes  and  large  bypass 
condensers  in  the  plate 
circuits  particularly. 

The  amplification 
curves  were  obtained 
by  the  substitution 
method  using  a  vacuum- 
tube  volt-meter.  A  50- 
kilocycle  voltage  from 
an  oscillator  is  impressed 
by  means  of  a  calibrated 
resistance  on  the  input 
of  the  single  stage  and  a 
reading  is  taken  on  the 
vacuum-tube  voltmeter 
connected  in  the  plate 
circuit  of  the  detector. 
Then  the  stage  is  cut 
out  and  a  second  voltage 
is  impressed  upon  the 
input  terminals  of  the 
detector  of  such  a  value 
as  will  give  the  same 
reading  on  the  volt- 
meter. This  input  volt- 
age will  be  larger  than 
when  the  stage  of  ampli- 
fication is  used  and  if 
the  current  through  the 
variable  resistances  is 
kept  the  same  in  both 
cases,  the  voltage  im- 
pressed will  be  directly 
proportional  to  the 
corresponding  values  of 
resistance.  The  ratio  of 

the  value  of  resistance  used  without  the  stage  of 
amplification  to  the  value  of  resistance  used 
with  the  stage  of  amplification  gives  the  voltage 
amplification  of  the  stage.  All  measurements  are 
made  with  the  oscillator  tube  removed  from  its 
socket  and  a  resistance  of  10,000  ohms  is  placed 
in  series  with  the  test  leads  from  the  calibrated 
resistance  to  represent  the  plate  resistance  of  the 
first  detector  which  is  normally  shunted  across 
the  primary  of  the  input  transformer. 

As  has  been  mentioned,  the  amplifier  is  for 
code  reception  with  any  autodyne  receiver  and 
it  may  either  be  connected  in  place  of  the  primary 
of  the  audio-frequency  transformer  of  the  re- 
ceiver, or  more  simply  by  connecting  its  input 
terminals  in  series  with  the  positive  detector  B- 
battery  lead  of  the  receiver. 

The  operation  of  the  complete  receiver  is  no 
more  complicated  than  the  operation  of  the 


r.f.  stage  with  or 
forms  of  coupling 


usual  two-control  short-wave  outfit.  The  first 
three  dials  of  the  amplifier  are  set  at  about  the 
same  values  and  a  station  tuned-in  on  the  re- 
ceiver while  the  oscillator  dial  is  varied  to  give 
the  desired  note.  The  first  three  dials  are  read- 
justed carefully  for  maximum  volume.  Now  the 
entire  amplifier  can  be  left  untouched,  all  the 
tuning  being  done  with  the  tuning  and  regenera- 
tion controls  of  the  short-wave  receiver.  The 
regeneration  switch  on  the  amplifier  can  be  used 
as  a  rough  volume  and  selectivity  control. 

If  the  receiver  described  by  the  author  on 
pages  13  and  14  is  to  be  operated  with  the  screen- 
grid  super-heterodyne  unit,  the  following  state- 
ments hold.  Because  of  the  fact  that  the  variable 
condenser  across  the  secondary  of  the  input 
transformer  of  the  super-heterodyne  unit  is 
mounted  directly  on  the  aluminum  shield,  the 
ground  post  of  the  shields  of  the  super-hetero- 
dyne cannot  be  directly  grounded  to  the  positive 
A  battery  but  can  be  done  so  through  a  i-mfd. 
fixed  condenser.  This  is  necessary  because  the 
copper  shield  of  the  receiver  is  necessarily 
grounded  to  the  positive  side  of  the  A  battery 
while  the  first  aluminum  shield  of  the  "super" 
has  been  connected  to  the  negative  side  of  the 
battery.  When  using  the  two  sets  together,  then, 
the  positive  side  of  the  A  battery  is  grounded 
and  the  shields  of  the  "super"  are  connected  to 
the  positive  A  binding  post  through  the  large 
condenser. 

The  following  parts  were  used  in  the  con- 
struction of  the  super-heterodyne  unit: 

LIST  OF  PARTS 

T  — Special  Input  Transformer  (See  Text) 
TI — Samson  Audio  Transformer,  6-1  Ratio 
L  — Two  Samson  No.  85  Choke  Coils 
LI — Five  Samson  No.  3  Choke  Coils 
U — 25-Turn  Tickler  Coil  (See  Text) 
U — Special  Oscillator  Coil  (See  Text) 
C  — Four   500-mmfd.   National   Variable   Con- 
densers 

Ci — Four  2ooo-mmfd.  Sangamo  Fixed  Conden- 
sers 

Ci — Three    looo-Mmfd.   Sangamo    Fixed   Con- 
densers 

Ca — Five  i-mfd.  Dubilier  Fixed  Condensers 
R  — Two  1 5-Ohm  Carter  Fixed  Resistances 
Ri — loo.ooo-ohm  Tobe  Resistor  with  Mounting 
Ra — 4-Megohm     Durham     Grid     Leak     with 

Mounting 

Ra — 2-Ohm  General  Radio  Rheostat 
Five  General  Radio  Sockets 
Yaxley  Filament  Switch 
K— Yaxley  S.P.D.T.  Jack  Switch 
Carter  Midget  Open-Circuit  Jack 
Ten  Eby  Engraved  Binding  Posts 
Four  4"  National  Velvet  Vernier  Dials 
White  Pine  Baseboard  23!"  by  10"  by  J" 
Bakelite  Panel  24"  by  7"  by  Ty 
Aluminum  Shields,  Extension  Shafts.  Insulating 
Pillars,   Angles,   Wood   Screws,  Etc 


A    PANEL    VIEW    OF    THE    SHORT-WAVE    "SUPER"    UNIT 

Despite  the  number  of  dials  on  the  panel,  the  receiver  is  no  more  difficult  to  tune  than  the  ordinary 
two-control  short-wave  receiver.  After  the  dials  on  the  super-heterodyne  unit  have  once  been  set, 
all  the  tuning  is  done  by  means  of  the  controls  of  the  short-wave  receiver  which  precedes  the  "super" 


Ourpur 


Condensers 
I 


b&C 
Terminals 


R4 


R3      UX-201-A  UX-171 

(CX-301-A)       (CX-371 

THE  SIMPLICITY  OF  THE  D.C.  AMPLIFIER  IS  EVIDENT  FROM  THIS  PHOTOGRAPH 


Irrpuh 


-A 
-A) 


By  Victor  L.  Osgood 


THE  problem  of  getting  really  fine  tone 
quality,  power,  and  volume  from  an  am- 
plifier entirely  electrically  operated  from  a 
1 1 5-volt  direct-current  supply   is  one  that  has 
frequently  stumped  the  fan  who  does  not  live  in 
a  district  where  a.c.  is  available.  Many  still  be- 
lieve that  it  is  not  possible  to  do  away  with  B 
batteries  where  the  supply  is  d.c.  in  nature,  and 
still  get  good  quality  and  volume. 

The  problem  for  a  time  was  a  baffling  one,  but 
the  introduction  of  power  tubes,  especially  those 
of  the  lyi-A  type,  has  made  possible  the  design 
of  a  power  amplifier  that  has  won  the  approval 
of  all  those  who  have  heard  it. 

The  solution  lies  in  combining  a  stage  of  trans- 
former-coupled amplification  with  a  second  stage 
of  push-pull,  using  two  tubes  in  parallel  on  each 
side  of  the  push-pull  system.  Ninety  volts  are 
placed  on  the  plate  of  the  first  tube  (a  ux-aoi-A 


About  the  Amplifier — 

THE  majority  of  self-contained  electrically- 
operated  receivers  now  on  the  market  are  designed 
to  function  by  plugging  into  an  alternating-current 
source.  While  there  are  some  manufactured  receivers 
now  available  for  use  where  the  supply  is  d.c.,  these 
are  few  and  far  between.  Constructional  articles  on 
d.c.  equipment  have  been  equally  scarce,  mainly  due 
to  the  fact  that  the  districts  where  d.c.  is  supplied 
are  considerably  in  a  minority.  The  combined  power 
amplifier  and  power-supply  unit  described  in  this 
article  is  especially  for  the  much-neglected  con- 
structor whose  house  supply  is  d.c.  It  will  handle  as 
much  undislorted  output  as  will  a  single  171  type 
tube  with  180  volts  on  the  plate  and  40.5  volts  on  the 
grid — sufficient  for  ordinary  home  purposes. 

— THE  EDITOR 


-  Six  resistors 
in  series  -14.3  ohms  each 


B+90      B+67       Det       *Jo22%vMBMery         B~        V Gnd' 
Plate 


FIG.     I 


or  a  cx-3Oi-A)  with  a  grid  bias  of  4.5  volts,  and 
power  tubes  of  the  lyi-A  type  are  employed  in 
the  push-pull  system  with  a  plate  potential  of 
105  to  1 10  volts  and  a  grid  bias  of  22.5  volts.  The 
input  connection  to  the  amplifier  may  be  made 
directly  to  the  plate  of  the  detector  tube  in  the 
receiver  itself.  Four  ux-171-A  (cx-3yi-A)  tubes 
are  used  in  the  push-pull  system,  as  shown  in  the 
schematic  diagram,  Fig.  I,  and  they  can  supply 
an  output  of  700  milliwatts  to  the  loud  speaker. 
This  will  be  found  ample  to  give  excellent  tone 
quality  and  volume.  A  push-pull  amplifier  some- 
times has  a  tendency  to  oscillate  and  for  this 
reason  a  25,ooo-ohm  resistance,  R3,  is  connected 
in  the  center  tap  lead  of  the  input  push-pull 
transformer  to  absorb  any  unbalance  in  the  cir- 
cuit which  would  otherwise  tend  to  make  the 
amplifier  oscillate.  The  filaments  of  the  I7I-A 
type  tubes  in  the  power  amplifier  are  lighted  with 
power  obtained  from  the  1 1 5-volt  line  after  the 
voltage  has  been  reduced  by  resistance  Ri. 

The  circuit  is  arranged  so  that  plate  potential 
for  the  radio-frequency  amplifying  tubes  and  the 
detector  is  available;  thus  the  necessity  for  B 
batteries  is  altogether  eliminated. 

Even  though  the  supply  is  d.c.  some  filtering  is 
necessary  to  eliminate  the  commutator  ripple  in 
the  voltage.  The  filter  circuit  used  here,  however, 
is  very  simple,  consisting  of  one  choke  coil,  L,, 
and  a  4-mfd.  filter  condenser,  Ci.  Two  i-mfd. 
bypass  condensers,  G>  and  C3,  are  also  necessary 
across  the  two  intermediate  voltage  taps.  The 
d.c.  voltage  rating  of  these  condensers  need  not 
be  more  than  160  volts.  Either  67  or  90  volts  are 
available  for  the  plate  circuits  of  the  r.f.  ampli- 
fiers, the  choice  of  voltage  depending  upon  the 
individual  set  and  the  owner's  preference. 

Biasing  voltages  are  supplied  by  dry  batteries. 
Were  we  to  take  the  required  22.5  volts  C  bias 
from  the  power  line,  we  would,  of  course,  have  to 
deduct  just  that  much  from  the  total  voltage 


18 


THE    RIGHT     ,W.fk>fUw    GO 


ATION 


By  L.  W.  Hatry 


M' 


"ANY  set  builders  have  searched  for  the 
ideal  form  of  amplification  by  plodding 
their  way  through  combinations  of  re- 
sistance, impedance,  and  transformer  coupling, 
attempting  to  effect  a  compromise  between  the 
supposed  quality  of  one  system  and  the  well- 
known  high  step-up  ability  of  another.  Or,  at 
times,  the  search  for  perfection  may  have  been 
tinctured  with  the  desire  for  a  combination  which 
made  use  of  apparatus  already  on  hand. 

Whatever  the  reasons  for  such  combinations, 
they  should  be  made  only  with  some  apprecia- 
tion of  the  apparatus  and  its  limitations.  Many 
persons,  for  instance,  wonder  where  in  an  a.f. 
system  to  place  the  audio  transformer  if  only  one 
is  used.  The  answer  to  such  questions  can  always 
be  found.  The  method  is  simple. 

Consider  that  the  voltage  step-up: 
(i.) — in  a  20 1 -A  is  8. 
(2.) — in  a  199  is  6. 
(3.) — through  a  resistor-coupler  is  I. 
(4.) — through  an  impedance-coupler  is  i 
(5.) — through  a  transformer  is  2,  3,  3j, 
according    to    the    step-up    ratio 
windings. 

(6.)— through  a  high-mu  tube  (240  type)  is  about 
20,  or  through  any  tube  in  a  resistance-  or 
impedance-coupled  stage  ought  to  be  about 
two-thirds  of  the  tube's  mu  (we  have  taken 
the  effective  step-up  to  be  six  in  the  case  of 
a  2O1-A  type  tube). 

This  information  is  available  in  magazines,  in 
catalogues,  in  tube  instruction  sheets,  and  in  text- 
books. It  allows  one  to  engineer  his  a.f.  amplifier 
with  the  employment  of  something  akin  to  in- 
telligence and  the  enjoyment  of  a  feeling  near 
that  of  competence. 

As  a  preliminary  to  this  engineering  feat, 
choose  some  audio  system  you  know  to  be  func- 
tioning in  a  way  that  satisfies.  As  an  example, 
let  us  use  a  two-stage  amplifier  with  3  to  I  and 
6  to  i  audio  transformers,  a  2OI-A  in  the  first 


5,  or  6, 
of    the 


__..^_   r?nrl   Thi-    Pnv    Pi  !•*:<•_______ 

Cr'HE    signal   voltage    handling   capacity   of  a 
J.  tube  used  as  an  audio  amplifier  is  governed 

by  the  amount  of  bias  placed  on  that  tube's  grid. 
Thus,  a  2O/-A  type  tube,  with  4.5  volts  bias  (and 

the  corresponding  plate  roltage  of  90)  will  be  over- 

loaded and  distort  if  called  upon  to  handle  more 

than  4.5  peak  wits.  The  following  table  of  C  and 

B  battery  voltages  for  various  lubes  used  as  ampli- 

fiers will  serve  to  make  the  author's  article  more 

complete: 

TUBE  TYPE 

B  VOLTS 

C  VOLTS 

Mu 

45 

".5 

8.4 

67 

3 

8  4 

2O1  -A 

90 

45 

•5 

H5 

9 

8.5 

OO 

6 

7-9 

I  12 

"35 

0 

8.2 

157 

10.5 

8.2 

00 

.6.5 

3 

I?' 

'35 

27 

2.9 

180 

40.5 

29 

90 

4-5 

7-  5 

210 

'35 

9 

/   •> 

1  80 

10 

7-5 

222 

180 

>   5 

60 

stage,  and  a  171  in  the  second  stage,  as  shown  in 
Fig.  i.  The  power  tube  is  getting  a  B  voltage  of 
180  and  is  properly  biased  so  it  is  important  to 
remember  that  its  grid-swing  limit  is  about  40 
volts  peak.  To  load  the  power  tube,  the  second 
a.f.  transformer  must  supply  this  40  volts.  We 
shall  now  determine  the  characteristics  of  an 


amplifier  which  will  fulfill  this  requirement.  For 
the  second  or  the  final  audio  transformer  to  give 
40  volts,  the  grid  of  the  tube  in  the  first  stage 
must  be  getting  a  voltage  equal  to  40  divided 
by  the  turns  ratio  of  the  transformer  and  the  mu 
of  the  tube.  The  overall  gain  of  the  amplifier 
in  Fig.  i  will  be: 

T     Vt  =  zoi-A     T 
3X8       X      6  =  144 

Thus  the  requisite  voltage  at  the  output  of  the 
detector  must  be:  •  • 

-^  =  0.28  VOLTS 
144 

For  sake  of  argument  we  shall  accept  this  value 
of  0.28  volts  as  being  average  in  future  calcula- 
tions. It  has  been  the  writer's  observation,  how- 
ever, that  many  signals  overload  the  171  with  an 
amplifier  of  this  type,  which  would  indicate  that 
the  output  voltage  of  the  detector  sometimes 
exceeds  0.28  volts.  This  holds  true  for  a  set  in 
Hartford,  Connecticut,  which,  of  course,  is  com- 
paratively surrounded  with  high-powered  broad- 
casters. If  the  detector  will  put  out  0.56  volts, 
twice  that  calculated  above,  we  can  use  a  3  to  i 
transformer  instead  of  the  6  to  i  transformer 
in  Fig.  i  with  somewhat  better  frequency  charac- 
teristics. 

Presuming  that  the  a.f.  amplifier  will  be  satis- 
factory if  up  to  the  grid  of  the  power  tube  it  has 
a  voltage  multiplying  ability  of  144,  the  business 
of  figuring  equivalent  combinations  of  resistance 
or  other  couplings  is  easy.  For  instance,  in  a  three- 
stage  resistance-coupled  amplifier,  such  as  is 
shown  in  Fig.  2,  using  2OI-A  tubes,  the  gain  up 
to  the  grid  of  the  power  tube  will  be  (bearing  in 
mind  that  a  resistor-coupler  has  a  gain  of  i  and 
that  the  actual  amplification  through  the  tube 
is  about  two-thirds  of  its  mu): 


Re 


Vt  =  2oi-A 
X      6       X 


Vt 
X 


•  201-A       Re 

6       X        i   • 


If  the  second  tube  has  a  grid  bias  of  4.5  volts 


Del. 


FIG.    I 


FIG.    2 


24 


RADIO  BROADCAST 


MAY,  1928 


and  the  correspondingly  correct  B  voltage  (in 
which  case  it  should  not  be  called  upon  to  handle 
more  than  4.5  volts  signal  voltage),  it  would  be 
overloaded  when  required  to  handle  the  six  volts 
which  would  deliver  36  a.f.  volts  to  the  grid  of  the 
final  tube.  This  latter  figure  is  not  even  enough 
to  load  up  a  171  fully.  The  bias  on  the  second 
tube  could  be  increased,  with  correspondingly 
greater  handling  capacity,  but  this  in  turn 
would  necessitate  a  higher  B-battery  voltage.  It 
will  be  seen,  therefore,  that  the  second  2OI-A 
audio  tube  would  be  nicely  loaded  with  a  4-volt 
grid-swing,  in  which  case  it  would  be  able  to 
supply  the  final  tube  with  24  grid  volts.  A  171 
type  tube  with  only  1356  volts  and  a  C  bias  of 
27  will  be  adequate  to  handle  these  24  volts. 
With  this  amplifier  the  detector  must  output 
0.67  volt  (24  •*•  36)  to  load  the  171,  which  is 
quite  a  lot,  if  for  no  other  reason  than  that  local 
stations  are  likely  to  be  necessary  for  so  high  a 
voltage.  It  will  be  agreed,  then,  that  the  usual 
resistance  coupled  amplifier  with  2OI-A  type 
tubes  is  not  very  satisfactory. 

But  suppose  we  use  240  type  high-mu  tubes 
with  a  working  mu  of  20.  Here  are  the  figures: 


Re      Vt 
i     X 


240       Re      Vt  =  240       Re 
>      X       i      X      20      X      i  =400 


The  240  will  take  a  grid-swing  of  3  (with  180 
volts  B,  3  volts  C).  It  can  overload  a  171  on  180 
volts  if  it  gets  more  than  2  grid  volts  because  2 
multiplied  by  20  (the  gain  in  the  tube)  is  equal 
to  40,  the  maximum  handling  capacity  of  the 
171.  Hence,  if  three  resistance-coupled  stages 
are  used,  and  since  we  have  already  decided  that 
an  amplification  of  144  will  satisfy  for  average 
conditions  of  detector  output,  the  use  of  240  type 
tubes  is  probably  foolish.  By  dropping  the  plate 
resistor  of  the  first  tube  to  100,000  ohms,  the 
latter's  step-up  can  be  reduced  to  about  12. 
That  would  give  an  overall  step-up  of  240  to  the 
grid  of  -the  last  tube.  A  2OI-A  type  tube  in  the 
first  stage,  with  a  step-up  of  only  6,  will  reduce 
the  overall  gain  to  120,  which  begins  to  fit  better 
with  the  desirable  figure. 

Now  let  us  consider  a  single  resistance-coupled 
stage.  There  has  been  a  lot  said  about  it  in  some 
of  the  more  active  sections  of  the  press: 

Re      Vt  =  240      Re 

I       X       20       X         I      =  20 

That  is  obviously  no  good.  Why?  The  detector 
would  have  to  output  2  volts  in  order  to  put 
40  volts  on  the  grid  of  the  power  tube.  What 
about  one  resistance-coupled  and  one  transformer 
coupled  stage,  such  as  that  shown  in  Fig.  3? 

T      Vt  =  240      Re 
3     X     20      X      i    =  60 

It  will  be  seen  that  the  gain  is  insufficient  in  such 
a  combination,  too  great  a  detector  output  being 
necessary.  If,  however,  the  transformer  were  a 
high-grade  6  to  i  unit  instead  of  a  3  to  I  unit,  the 
overall  gain  would  be  120,  which  is  much  better. 
Now  let  us  consider  the  following  three-stage 
a.f.  amplifiers,  shown  in  Figs.  4  and  5,  in  which 


Det. 


FIG.  3 


the  second  audio  tubes  will  handle  about  4.5 
volts  grid  voltage  (since  they  are  biased  accord- 
ingly): 


T      Vt 
3      X 


Vt  =  201-A 
X       6        X 


Re 


Re 


Vt  =  2oi-A 
X       6       X 

Vt  =  2oi-A 

X       8       X 


Re 

i   =  108 


T 
3    =  144 


the  gain  of  the  amplifier,  the  smaller  the  detecto/ 
output  voltage  necessary  to  load  up  the  power 
tube.  Various  three-stage  combinations,  with 
their  overall  amplification,  are  listed  below.  The 
necessary  C  voltage  for  the  tubes  may  be  de- 
termined by  reference  to  the  table  on  page  23. 


In  the  first  case  the  next-to-the-last  tube  will  be 
badly  overloaded  if  the  signal  is  strong  enough 
to  load  a  171  to  its  maximum  handling  capacity 
of  40  grid  volts.  In  practice,  of  course,  the  volume 
control  on  the  receiver  would  be  turned  down  as 
soon  as  overloading  of  the  2O1-A,  manifest  as 
distortion,  became  apparent,  and  thus  the  171 
would  be  working  uneconomically.  To  deliver 
40.5  volts  to  the  171  the  next-to-the-last  tube 


Re       Vt  =  240 


Re       Vt  =  240 
l       X       20      X 


Re 


400 


Re 

Vt  =  2oi-A 

T 

Vt  = 

20  1  -A 

T 

i 

X       8 

X 

3 

X 

8      X 

3 

=   576 

Re 

Vt  =  20 

[-A 

T 

Vt  = 

201-A 

T 

i 

X       8 

X 

2 

X 

8      X 

2 

=   256 

Re 

Vt  = 

201  -A 

T 

Vt  = 

=   201-A 

T 

i 

X 

8 

X 

2 

X 

8     X 

3 

=   384 

Re 


Vt  =  240 
X      20      X 


Re 


Vt  =  201-A      T 

X       8      X       3  =480 


FIG.    4 


has  to  handle  6.75  volts  on  the  grid.  If  this  tube 
were  given  a  raise  in  bias  to  g  volts  with  135 
plate  volts,  it  would  be  capable  of  handling  this 
voltage  without  overloading.  Merely  moving  the 
a.f.  transformer  to  the  third  coupling  position,  as 
in  Fig.  5,  requires  that  the  second  audio  tube 
have  a  grid- voltage  of  only  1.68  to  produce  40.5 
volts  on  the  grid  of  the  power  tube. 

Judging  from  the  fact  that  many  set  owners 
find  two  high-mu  tubes  highly  desirable  in  a 
resistance — or  impedance-coupled  amplifier,  the 
opinion  that  an  amplifier  step-up  of  400  is  some- 
times useful,  seems  logical.  Of  course  the  higher 


From  all  of  the  foregoing  come  a  few  useful 
rules,  which  may  be  outlined  as  follows: 

(i.)  In  a  combination  of  transformer-coupling 
with  any  other  type  of  audio-frequency  amplifi- 
cation the  transformers  should  be  in  the  last 
stages,  and  the  transformer  with  the  greatest 
step-up  should  be  in  the  last  one. 

(2.)  Always  make  certain  that  the  tube  before 
the  power  tube  will  not  be  overloaded  before  the 
power  tube  is  fully  loaded.  To  find  this  out  is 
merely  a  matter  of  simple  division  or  multiplica- 
tion. 

(3.)  When  judging  the  performance  of  two  am- 
plification systems,  calculate  what  the  overall 
step-up  for  each  is  before  deciding  what  has  hap- 
pened. 

There  are  other  simple  rules  that  it  is  good  prac- 
tice to  heed.  They  may  be  stated  as  follows: 

(a.)  It  is  always  best  to  require  least  of  the 
detector.  This  is  possible  when  the  a.f.  step-up 
is  high. 

(b.)  High  a.f.  step-up  is  no  help  to  the  detector 
if  the  volume  control  follows  the  detector,  and 
the  less  the  step-up  in  the  audio  end  the  more 
this  is  true. 

(c.)  A  detector  gives  greater  undistorted  out- 
put with  increased  B  voltage,  within  limits. 
Operate  it  according  to  the  needs  of  your 
set. 


A    $IO,OOO    PHONOGRAPH-RADIO    COMBINATION 

The  phonograph  equipment  is  housed  at  the  left  and  the  radio  at  the  right.  The  panel  in  the  center 
contains  a  distortion  meter  (reading  up  to  150  mils.)  and  special  circuit  arrangements  make  it  possi- 
ble to  control  the  amplitude  of  the  sound  by  the  top  knob  in  this  panel,  while  the  control  directly 
below  it  regulates  overtones.  The  installation  uses  a  four-stage  balanced  amplifier  rated  at  50  watts. 
Individual  expression  in  the  rendition  of  phonograph  records  or  radio  is  said  to  be  achieved  through 
circuits  arranged  to  vary  both  musical  pitch  and  overtones  without,  at  the  same  time,  altering  quality. 
This  installation  was  especially  built  for  La  Salle  &  Koch,  of  Toledo,  Ohio 


C  If  K>  THE  great  American  query,  "What's 

I  new?"  we  are  forced  to  reply  this  month, 
•*-  "Not  much."  It  may  be  merely  an  off- 
season for  records.  There  were  all  too  few  likely 
looking  titles  in  the  advance  lists.  Perhaps  the 
phonograph  industry,  like  book  publishing, 
blooms  in  full  glory  but  twice  a  year  and  in- 
between-times  puts  out  only  a  few  pale  buds. 
No,  it  isn't  quite  as  bad  as  that  because  we  did 
find  nine  records  of  such  exceptional  merit  that 
they  quite  make  up  for  the  mediocrity  of  the 
rest.  Among  the  classical  output  are  several 
prize-winners:  two  duets  by  Gigli  and  De  Luca, 
who  can  always  be  counted  on  to  be  worth  while; 
two  beautiful  songs  by  Sigrid  Onegin;  choral 
work  of  outstanding  quality  by  the  Metropolitan 
Opera  Chorus;  and  two  instrumental  numbers  by 
the  Columbia  Symphony  Orchestra.  Of  the  pop- 
ular stuff  there  are  five  better-than-average 
records.  Ohman  and  Arden  performing  Gersh- 
win music;  Johnny  Johnson  and  His  Statler 
Pennsylvanians  offering  another  Gershwin  num- 
ber and  on  the  reverse  one  of  the  best  songs  from 
the  Connecticut  Yankee;  a  Paul  Whitman  mas- 
terpiece; two  good  numbers  from  the  orchestra 
directed  by  the  Maestro,  known  to  the  trade  as 
Ben  Bernie;  and,  lastly,  a  couple  of  unusual 
waltzes  by  the  South  Sea  Islanders.  The  rest  are 
so-so. 

'S  Wonderjul  and  Funny  Face  by  Victor  Arden 
and  Phil  Ohman  and  Their  Orchestra  (Victor). 
Superb  Gershwin  music  mixed  well  with  Ohman- 
and-Arden  piano  magic  and  flavored  with  a  bit 
of  Johnny  Marvin's  best  singing. 

Thou  Swell  and  My  One  and  Only  by  Johnny 
Johnson  and  His  Statler  Pennsylvanians  (Vic- 
tor). Tuneful  antidotes  for  that  poisonous  late- 
winter  boredom. 

Mary  and  Changes  by  Paul  Whiteman  and 
His  Orchestra  (Victor).  Whiteman  continues  to 
glorify  American  jazz. 

The  Man  I  Love  and  Dream  Kisses  by  Ben 
Bernie  and  His  Hotel  Roosevelt  Orchestra 
(Brunswick).  This  record  deserves  a  great  big 
gold  star. 


I've  Been  Looking  for  a  Girl  Like  You  and 
Everywhere  You  Go  by  Paul  Ash  and  His  Orches- 
tra (Columbia).  For  those  who  crave  their  jazz 
red  hot. 

Changes  and  Let's  Misbehave  by  Ben  Bernie 
and  His  Hotel  Roosevelt  Orchestra  (Brunswick). 
Keeping  up  with  the  Bernie  tradition  of  bigger, 
better  dance  music,  with  the  emphasis  on  dance. 

We'll  have  a  New  Home  and  When  'You're  With 
Somebody  Else  by  Ben  Selvin  and  His  Orchestra 
(Columbia).  Standard  fox  trots  of  the  snappy 
variety  dressed  up  with  fancy  orchestration. 

Tomorrow  and  I'm  Making  Believe  That  I 
Don't  Care  by  the  Colonial  Club  Orchestra 
(Brunswick).  Just  like  countless  other  plaintive 
waltzes. 

Girl  of  My  Dreams  I  Love  You  and  Sugar 
Babe,  I'm  Leavin'!  by  Blue  Steele  and  His  Or- 
chestra (Victor).  One  more  waltz  and  a  noisy 
foxtrot  with  a  raucous  vocal  chorus. 

The  Man  I  Love  by  Fred  Rich  and  His  Hotel 
Astor  Orchestra  (Columbia)  A  good  song  handled 
with  no  particular  merit.  For  My  Baby  by  Leo 
Resiman  and  His  Orchestra.  If  your  doctor  has 
tactfully  suggested  that  you  do  more  exercising, 
get  this  record.  You  can't  sit  still  to  this  number. 

/  Ain't  Got  Nobody  and  Weary  Blues  by  Ray 
Miller  and  His  Hotel  Gibson  Orchestra  (Bruns- 
wick). Right  you  are!  The  first  is  an  old  number 
and  what's  more  it  is  played  in  the  old  fashioned 
way  with  lots  of  brass  and  much  pep.  Of  the 
second — the  only  thing  that's  weary  must  be 
the  orchestra  after  it  finishes. 

When  the  Robert  E.  Lee  Comes  to  Town  and  / 
Scream,  You  Scream,  We  All  Scream  for  Ice 
Cream  by  Harry  Reser's  Syncopators  (Colum- 
bia). If  you  haven't  heard  the  words  to  the  latter 
song  the  record  is  worth  listening  to — once. 

Dawn  and  We  Two  by  The  Troubadours  (Vic- 
tor). Lewis  James  and  F.d  Smalle  who  manipu- 
late the  vocal  refrains  and  the  Troubadours  have 
between  them  made  a  grand  record  out  of  two 
fairly  good  musical  comedy  numbers. 

Among  My  Souvenirs  and  Keep  Sweeping  the 
Cobwebs  Off  the  Moon  by  Abe  Lyman's  Califor- 

25 


The 

^Month's  New 
'Phonograph 


nia  Orchestra.  (Brunswick).  The  treatment  of 
the  first  is  perfectly  orthodox  which  means  good. 
The  second  leaves  us  cold. 

Away  Dawn  South  in  Heaven  and  There's  a 
Rickety  Rackety  Shack  by  Frank  Black  and  His 
Orchestra  (Brunswick),  (a)  Even  if  this  were 
good  we  wouldn't  like  it.  Not  with  that  vocal 
chorus!  (b)  Something  else  again;  it's  good! 

That's  (That  the  Lei  Said  to  Me  and  The  Call  of 
Aloha  by  the  South  Sea  Islanders  (Columbia). 
Waltzes  that  are  waltzes. 

Poor  Litfie  and  /  Love  to  Catch  Brass  Rings  on 
a  Merry-Go- Round  by  Billy  Jones  and  Ernest 
Hare  (Columbia),  a.  The  Happiness  Boys  sing 
out  the  old  and  sing  in  the  new  (Ford),  b.  Not 
very  good  nonsense. 

More  or  Less  Classical 

Pescatore  Di  Perle — Del  Tempio  Al  Limitar 
(Pearl  Fishers— In  the  Depths  of  the  Temple) 
(Bizet)  and  Cioconda — Enjo  Grimaldo,  Principe 
Di  Santafior  (En%o  Grimaldo,  Prince  of  Santafior) 
(Ponchielli).  Sung  by  Beniamino  Gigli  and  Giu- 
seppe De  Luca  (Victor).  Week-day  words  are 
inadequate  to  describe  the  exquisite  beauty  of 


Recommended  New  Records 

Pescatore  Di  Perle — Del  Tempio  Al  Limitar 
(Bizet)  and  Gioconda — En^o  Grimaldo, 
Principe  Di  Santafior  (Ponchielli)  sung  by 
Beniamino  Gigli  and  Giuseppe  De  Luca 
(Victor). 

The  Blind  Ploughman  and  The  Fairy  Pipers 
sung  by  Sigrid  Onegin  (Brunswick). 
Die  Zauberflote — 0  Isis  Und  Osiris  (Mo- 
zart) and  Chorus  of  Courtiers — on  Mischief 
Bent   (Verdi),   sung  by   the   Metropolitan 
Opera  Chorus  (Victor). 
Bridal  Procession  (Grieg)  and  March  of  the 
Bojaren  (Halvorsen)  played  by  the  Colum- 
bia Symphony  Orchestra.  (Columbia). 
'S  Wonderful  and  Funny  Face  by  Victor 
Arden  and  Phil  Ohman  and  Their  Orches- 
tra (Victor). 

Thou  Swell  and  My  One  and  Only  by 
Johnny  Johnson  and  His  Statler  Pennsyl- 
vanians  (Victor). 

Mary  and  Changes  by  Paul  Whiteman  and 
His  Orchestra  (Victor). 
The  Man  I  Love  and  Dream  Kisses  by  Ben 
Bernie  and  His  Hotel  Roosevelt  Orchestra 
(Brunswick). 

Jupiter  Symphony  (No.  41,  Op.  551) 
(Mozart)  by  the  State  Opera  Orchestra  of 
Berlin,  conducted  by  Richard.  Strauss. 
(Brunswick). 


26 


RADIO  BROADCAST 


MAY,  1928 


these  duets  as  sung  by  this  baritone  and  tenor 
from  the  Metropolitan  Opera  Company. 

The  Blind  Ploughman  (Radclyffe-Hall- 
Clarke)  and  The  Fairy  Piper  (Weatherly- 
Brewer)  sung  by  Sigrid  Onegin  (Brunswick). 
An  organ  accompanies  this  rich  contralto  voice 
in  the  first  selection  and  reflects  the  seriousness 
of  the  song.  In  the  second  selection  the  tinkling 
notes  of  a  piano  and  a  flute  illustrate  the  fairy 
music  of  which  Miss  Onegin  sings  delightfully 
as  well  as  capably. 

Lucia:  Sextet — Chi  raffrena  il  mio  furore  (Why 
do  I  my  arm  restrain?)  (Donizetti)  Sung  by  M. 
Gentile,  D.  Borgioli,  G.  Vanelil,  S.  Baccaloni, 
G.  Nessi,  1.  Mannarini  and  chorus.  (Columbia). 
This  imported  recording  does  not  do  full  justice 
to  the  famous  musical  race  in  which  the  soprano 
is  foreordained  to  win.  The  volume  is,  for  one 
thing,  too  great.  On  the  reverse  is  Somnambula: 
D'un  Pensiero  (No  Thought  but  for  thee)  by  M. 
Gentile,  D.  Borgioli,  I.  Mannarini,  G.  Pedroni 
and  chorus,  which  is  excellent  except  for  the 
thinness  of  the  soprano  voice. 

Die  Zauberflote — O  his  Und  Osiris  (The  Magic 
Flute — Chorus  of  Priests)  (Mozart).  Sung  by  the 
Metropolitan  Opera  Chorus  with  the  Metropoli- 
tan Opera  House  Orchestra  under  the  direction 
of  Giulio  Setti.  (Victor).  This  splendid  organi- 
zation presents  a  very  plausible  chorus  of  priests 
who  are  evidently  all  superior  musicians.  And 
the  very  next  moment  (on  the  reverse  of  the 
record)  they  are  equally  convincing  as  a  Chorus 
of  Courtiers — On  Mischief  Bent  (Scorrendo  Unili 
Remola  Via)  from  Verdi's  Rigoletto. 

My  Message  and  Nocturne  by  John  Charles 
Thomas  (Brunswick).  The  same  glorious  bari- 
tone— and  you  may  like  the  ballads. 

Quartet  in  G  Minor  Second  and  Fourth  Move- 
ments (Debussy).  Played  by  the  New  York 
String  Quartet  (Brunswick).  All  the  tricks  of  the 
string  trade  are  herein  utilized  to  demonstrate 
the  beautiful  and  varied  effects  obtainable  by 
two  violins,  a  viola  and  a  cello. 

Bridal  Procession  (Grieg;  Op.  19,  No.  2)  and 
March  of  the  Bojaren  (Halvorsen).  Played  by  the 
Columbia  Symphony  Orchestra  under  the  direc- 
tion of  Robert  Hood  Bowers  (Columbia).  This 
delightfully  gay  and  lighthearted  bridal  chorus 
must  have  been  written  for  a  fairy  wedding; 


mortals  take  their  weddings  more  tearfully. 
And  here  is  a  march  that  is  not  impressed  with 
its  own  importance  but  is  quite  willing  to  be  ex- 
uberant and  even  humorous.  But  then  a  march 
scored  for  strings,  and  woodwinds  as  well  as  for 
brasses  can  present  these  characteristics  more 
easily  than  can  the  fife  and  drum  brigade.  The 
Columbia  Symphony  handles  both  these  num- 
bers with  ability. 

All  Hail  the  Record  Albums 

IT  IS  just  another  miscarriage  of  justice  that 
somewhere  in  these  United  States  there  walks 
a  man,  unheralded  and  unsung.  The  man 
in  question  is  the  inventor  of  the  album  set. 
Until  he  sold  his  idea  to  the  phonograph  com- 
panies (we  hope  he  sold  it;  if  he  can't  have  fame 
he  should  at  least  have  royalties)  our  record 
library  contained  only  selections  from  operas, 
gems  from  operettas,  arias,  ballads,  folk  songs, 
bits  of  this,  and  bits  of  that.  No  extended  work 
could  be  had  in  its  entirety  because,  alas,  it 
could  not  be  fitted  on  to  the  limited  space  af- 
forded by  a  rubber  disc,  and  it  had  never  oc- 
curred to  the  phonographers  to  distribute  one 
work  of  art  over  several  discs,  selling  them  as  one 
unit.  Now,  however,  we  have  whole  symphonies, 
tone  poems,  and  concertos,  complete  from  the 
first  note  to  the  last.  They  come  on  several 
records,  neatly  stowed  away  in  good  looking 
albums,  and  accompanied  by  explanatory  book- 
lets which  invariably  are  excellent  and  use- 
ful. These  musical  works  are  recorded  by  the 
best  talent  available  in  this  country  and  in 
Europe  and  the  technical  work  of  putting  the 
notes  on  the  wax  is  done  so  expertly  that  no 
iota  of  tone  is  missing,  no  shading  is  lost. 

In  the  March  RADIO  BROADCAST  appeared  a 
partial  list  of  the  music  available  in  album  form. 
The  list  is  growing  daily. 

Mozart's  "Jupiter"  Symphony 

WE  HAVE  already  reviewed  one  album  set, 
the    Scheherazade    Symphonic    Suite    by 
Rimsky-Korsakov,  played  by  the  Philadelphia 
Orchestra  under  the  direction  of  Leopold  Sto- 
kowsky,  and  recorded  by  Victor.  This  month  we 


A    CLOSE-UP    OF    THE    CONTROL    PANEL 

A  bank  of  three  loud  speakers  is  used  with  this  phonograph-radio  combination.  Each  loud  speaker 

circuit  has  its  own  distortion  meter,  with  controls  permitting  each  circuit  to  be  operated  at  its  own 

regulated  volume.  Circuits  and  apparatus  are  provided  so  that  the  operator  can  announce  the  selection 

to  be  played  through  the  entire  loud  speaker  system 


praise  another  symphony,  equally  beautiful 
in  an  entirely  different  way,  the  Jupiter  Symph- 
ony (No.  41,  Op.  551)  of  Mozart,  played  by  the 
State  Opera  Orchestra  of  Berlin,  conducted  by 
Richard  Strauss,  recorded  in  Europe  for  Bruns- 
wick. It  covers  two  sides  of  three  records  and 
one  side  of  a  fourth,  the  remaining  surface  being 
given  over  to  the  Turkish  March  (Mozart-Cerne) 
played  by  Vasa  Prihoda.  The  Rimsky  symphony 
is  full  of  color,  warmth,  and  emotion.  It  con- 
jures up  pictures  of  the  Orient  with  its  glowing 
colors,  shimmering  light,  sinuous  maidens,  sway- 
ing camels,  dancing  fakirs,  and  the  spicy  smells 
of  the  market  place — all  the  kaleidoscopic  ro- 
mance of  the  East.  Mozart's  symphony,  on  the 
other  hand,  brings  forth  no  pictures.  It  lacks  the 
warm  humanity  of  the  Russian  music,  lacks  its 
emotion,  lacks  its  color.  But  it  has  something 
which  takes  the  place  of  these  qualities,  a  pre- 
cise musical  style.  It  is  music  as  pure,  unsullied, 
and  crystal  clear  as  water  bubbling  from  a 
spring  on  a  mountain  side.  It  is  melodious  from 
start  to  finish  for  Mozart  was  an  expert  harmon- 
ist. He  lived  his  short  life  (1756-1791)  at  a  time 
when  emphasis  was  placed  on  form  and  har- 
mony. The  symphony  was  a  fairly  recent  de- 
velopment. It  had  evolved  gradually  from  the 
overture,  the  instrumental  introduction  to  an 
opera,  and  had  been  given  a  more  or  less  stand- 
ard form  by  Haydn  who  was  born  twenty-four 
years  before  Mozart.  This  form  consisted  of 
three  or  four  movements,  generally  four.  The 
first  and  fourth  were  the  longer  and  more  es- 
sential, and  were  brisk  in  tempo.  The  second 
was  slower  and  eminently  lyrical,  and  the  third 
usually  a  sprightly  minuet.  This  is  the  form  used 
by  Mozart  in  the  Jupiter  Symphony.  The  or- 
chestra for  which  he  scored  the  symphony  con- 
sisted of  one  flute,  two  oboes,  two  bassoons,  two 
horns,  two  trumpets,  kettledrums,  and  strings, 
and  for  the  second  movement  he  reduced  it  by 
the  omission  of  trumpets  and  drums.  This  is  a 
much  smaller  organization  than  the  symphony 
orchestra  of  to-day. 

It  is  particularly  in  the  fourth  movement,  the 
loveliest  of  them  all,  that  Mozart  displays  his 
technical  skill,  but  not  ostentatiously.  The 
beauty  and  spontaneity  of  the  music  conceal  the 
learning  which  is  its  foundation.  The  design  of 
the  movement  is  a  combination  of  the  sonata 
form  and  the  fugue.  The  sonata  form  is  that 
used  for  first  movements  of  symphonies  and 
consists  of  three  parts,  the  Exposition  which 
sets  forth  the  themes;  the  Development  which 
embroiders  the  themes;  and  the  Recapitulation 
which  restates  the  themes.  In  this  movement 
Mozart  uses  four  distinct  musical  ideas.  The  first 
is  given  out  at  once  by  the  violins,  its  four 
opening  notes  being  an  ecclesiastical  melody  of 
which  Mozart  made  frequent  use.  A  second,  and 
gayer,  phrase  follows  this;  the  subject  is  then 
repeated  forte  by  the  full  orchestra  and  at  the 
end  of  the  passage  the  second  idea  is  introduced 
by  woodwind  and  strings.  There  are  sixteen  meas- 
ures of  this,  filled  with  exuberant  tone.  Next 
there  is  a  return  to  the  church  theme  treated  in 
the  orthodox  fugal  manner.  At  length  this  same 
theme  is  taken  up  forte  by  the  full  orchestra  and 
at  the  fourth  measure  of  it  there  is  heard,  in 
the  first  violins,  the  third  idea.  After  a  repetition 
of  the  second  idea,  the  fourth  idea — the  second 
real  theme — appears  in  the  strings. 

From  this  brief  analysis  of  the  last  movement 
of  the  symphony  you  can  perhaps  derive  some 
idea  of  the  intricacy  of  the  framework  on  which 
Mozart  weaves  his  beautiful  melodies.  You  will 
love  these  melodies  whether  or  not  you  under- 
stand the  construction,  but  if  you  follow  the 
mechanics  of  the  symphony  you  will  arrive  at 
a  more  complete  understanding  and  conse- 
quent appreciation  of  the  composition. 


'Detector 
Distortion 


MANY  TIMES  we 
have  read  about  radio 
receivers  so  engineered 
that  the  detector  did 
not  overload,  or  receivers  in  which  the 
detector  did  overload,  or  some  other  refer- 
ence to  distortion  due  to  detector  over- 
loading. This  leads  us  to  ask  such  ques- 
tions as:  When  does  a  detector  overload? 
What  does  the  output  sound  like  when 
such  overloading  occurs?  Is  it  true  that  a 
C  bias  detector  will  handle  much  larger 
input  voltages  without  overloading?  If 
so,  how  much?  The  answers  to  some  of 
these  questions  are  being  sought  in  the 
Laboratory,  and  as  fast  as  the  material 
is  ready  it  will  be  presented  in  these 
columns. 

In  the  meantime,  one  of  our  friends 
has  determined,  empirically,  that  the 
average  detector  begins  to  overload  when 
the  detector  delivers  about  15  TU  below 
i.o  milliwatt.  What  does  all  this  mean, 
you  will  ask? 

Let  us  suppose  that  a  detector  has  an 
output  impedance  of  30,000  ohms  and 
that  it  works  into  a  load  of  this  impedance, 
say  a  resistance  or  a  transformer  of  proper 
characteristics.  Fifteen  TU  below  i.o 
milliwatt  is  equal  to  about  0.03  milliwatts, 
or  about  30  microwatts.  What  voltage 
across  30,000  ohms  will  deliver  this 
amount  of  power?  This  is  the  useful  volt- 
age, for  it  is  what  the  amplifier  boosts 
in  value  so  that  the  final  power  tube  in  the 
system  will  deliver  its  rated  output. 
This  voltage  may  be  found  by  extracting 
the  square  root  of  the  product  of  the  power  by  the 
resistance.  Or. 


• 


rom 


E  =  VWoxK  =   v  0.03X10—  »X3",ooo  =  rvolt 
(approximately) 

Therefore,  a  detector  which  will  deliver  30 
microwatts  to  30,000  ohms  without  overloading 
will  produce  i.o  volt  across  the  input  to  the 
amplifier.  It  now  remains  to  prove  under  what 
conditions  the  detector  will  fulfill  these  expecta- 
tions, and  when  overloaded,  how  the  average 
experimenter  can  tell  it  by  the  sound  of  the 
output. 

Has  any  reader  experience  in  this  matter? 


<?4  Short-Wave 


THE  FOLLOWING  letter  ap- 
ropos  of  short-wave  experi- 
mental  broadcasting  and  its 
reception  is  interesting:  It 
comes  from  C.  R.  Strange,  of  Sydney,  Australia. 
"On  the  page  'Our  Readers  Suggest'  in  the 
December  RADIO  BROADCAST,  there  is  described 
'A  Short-Wave  Converter  for  any  Radio  Re- 
ceiver' by  Perry  S.  Graffam. 

"  It  will  be  of  interest  to  your  readers  to  know 
that  out  here  in  Australia  we  appreciate  your 
journal  and  that  several  days  ago  I  built  this 
adapter  to  plug  into  my  Grebe  Synchrophase 
which  was  presented  to  me  by  the  A.  H.  Grebe 
Company  of  Richmond  Hill,  New  York,  follow- 
ing my  reception  of  their  station,  WAHG,  on  314.5 
meters. 

"An  hour  after  I  had  finished  Graffam's 
adapter  I  was  listening  to  the  transmission  from 
2  LO  (London)  through  the  short-wave  station 
;  sw  Chelmsford  England,  on  24  meters,  using 
the  two  audio  valves  of  the  Synchrophase  re- 
ceiver and  my  model-  100  loud  speaker.  On  the 
25th  (January)  I  listened  wonderfully  to  this 
station  for  55  minutes,  the  volume  being  audible 
some  15  feet  from  the  speaker.  Also  on  the  25th 
and  last  night  1  listened  also  with  wonderful 
success;  here,  some  13,000  miles  away,  it  is  rather 
thrilling  to  listen  to  London  broadcasting  at 


midday  such  items  as  selections  from  Cavalleria 
Rusticana,  Percy  Grainger's  pianoforte  arrange- 
ments, Carmen,  and  a  fine  tenor  voice  singing 
'The  Sargent  Major's  on  Parade.' 

"We  surely  are  in  a  wonderful  age.  Televison 
will  be  the  next  thing  for  Australia." 

THERE  HAVE  been  numer- 
Short-Ware  ous  attempts  to  convince  the 

'Broadcasting  public  and,  we  imagine,  the 

Radio  Commission  as  well, 
that  broadcasting  should  take  place  on  the  high- 
frequency  (short-wavelength)  bands.  Let  us 
look  only  at  the  problem  of  keeping  a  station  on 
its  assigned  frequency  which,  for  sake  of  argu- 
ment we  shall  assume  to  be  10,000  kc.,  or  ten 
million  cycles.  Many  broadcasters  are  having 
difficulty  in  keeping  their  present  transmitters 
within  one-half  kc.  of  their  assigned  frequency. 
What  would  be  their  troubles  if  they  worked  at 
30  meters?  Five-hundred  cycles  in  10,000,000  rep- 
resents an  accuracy  of  one  part  in  20,000,  or  five- 
thousandth  of  one  per  cent.  At  the  present  time, 
a  station  operating  on  1000  kc.  must  keep  its 
assigned  frequency  to  within  500  cycles  in  one 
million  which  represents  one  part  in  2000  or 
five-hundredths  of  one  per  cent.  In  other  words, 
it  would  be  about  ten  times  as  difficult  to  keep  a 
station  on  its  frequency  at  30  meters  as  it  now 
is  at  300  meters. 

We  understand  the  Navy  builds  short-wave 
equipment  that  must  be  accurate  to  within  100 
cycles  at  30,000  kc.  That  is,  they  build  a  trans- 
mitter to  this  specification,  and  a  receiver  to  go 
with  it  and  the  sum  of  their  percentage  inaccu- 
racies must  not  be  over  200  cycles  in  10  million, 
or  100  cycles  for  the  individual  unit.  This  repre- 
sents an  accuracy  of  one  part  in  one  hundred 
thousand,  or  one  ten  thousandth  of  one  per  cent., 
an  accuracy  50  times  as  great  as  that  required 
of  stations  now  operating  within  the  broadcast 
band.  These  Navy  units,  it  should  be  noted, 
are  designed  for  code  transmission  and  recep- 
tion. 

29 


The  "Equamatic" 
System  in 
England 


RADIO  BROADCAST 
takes  pride  in  quoting 
part  of  a  letter  from 
Louis  G.  King,  whose 
system  of  tuning,  known  as  the  Equa- 
matic  System,  was  first  described  in  this 
magazine.  Mr.  King  has  just  returned 
from  Europe  and  that  his  trip  was  success- 
ful may  be  surmised  from  this  part  of  his 
letter:  "Recently  we  have  entered  into 
an  agreement  with  Graham  Amplion, 
Ltd.,  for  the  production  of  the  Equa- 
matic  System  in  the  British  Isles.  After 
carefully  testing  radio  receivers  produced 
by  the  leading  manufacturers  in  all  parts 
of  the  world,  Graham  Amplion,  Ltd., 
adopted  the  Equamatic  System."  The 
system  has,  in  this  country,  been  most 
closely  associated  with  receivers  designed 
by  the  Karas  Electric  Company. 


MANY  TIMES  in  the 

Finding  Ore  past  year  or  so,  the  edi- 

by  Radio  tors  have  been  asked 

to  forward  informa- 
tion on  devices  useful  in  finding  ore  or 
hidden  treasure  by  radio.  Up  to  the 
present  time  it  has  been  impossible  to 
give  any  authentic  information  regarding 
such  apparatus,  and  therefore,  we  are 
appealing  to  the  readers  of  the  magazine. 
What  is  wanted  is  information  on  methods 
and  apparatus  used,  whether  using  radio 
or  other  electrical  apparatus,  results  se- 
cured, and  articles  published  whether  in 
this  country  or  abroad.  This  will  enable 
us  to  help  prospective  treasure  hunters 
toward  a  financially  successful  jaunt. 


RADIO   LISTENERS   in  com- 
<Real  Power  munities   where   there   is   no 

firomtvioll2't  a.c.  power  available  need  not 

feel  that  it  is  impossible  to 
secure  sufficient  power  to  operate  their  loud 
speakers  properly  just  because  they  cannot  tap 
the  house  lighting  system  and  get  high  voltages 
and  considerable  plate  current  therefrom.  For 
example,  two  H2-A  tubes  will  deliver  consider- 
able power  without  excessive  plate  voltage  or 
current — which  means  that  the  farmer  who  has 
no  power  equipment  may  secure  good  quality 
and  plenty  of  loud  speaker  power  from  B  batter- 
ies, and  do  it  economically.  The  table  below  shows 
the  relative  power  output  and  necessary  grid  a.c. 
voltage  to  deliver  this  power  from  a  single  171 
or  two  ii2's  in  parallel.  Note  that  two  nz's 
in  parallel  with  157  volts  on  the  plate  require 
16  milliamperes  from  the  B  batteries  and  deliver 
400  milliwatts  of  power  to  a  loud  speaker  on 
only  10.5  input  grid  volts  while  a  171,  taking  the 
same  current  from  135  volts,  requires  a  grid  volt- 
age of  27  to  produce  350  milliwatts.  Two  i  I2's 
in  parallel  will  have  an  output  impedance  of 
about  2500  ohms  which  will  work  very  well  into 
the  average  loud  speaker: 

TUBE  EH  EC  IP  WATTS 

OUTPUT 

171  90  16.5  11  .12 
135  27  16  .35 
157  33  18  .50 
180  40.5  20  .65 


2—1 12's     90 
135 

157 


4.5 
9.0 

10.5 


8.0      .08 
11.6      .240 
16.0      .400 


SOME  TUBES  from  Sylvanh 

Tested  Products     Co.,     have     been 

^Products  measured  in  the  Laboratory 

recently.    The    values    given 

below  are  the  average  of  six  of  each  type  of  tube: 

TYPE  IP  n  Rp  GM  EP  EG 

201-A  2.2  9.2  12330  750  90  -4.5 

112-A  7.0  7.5  5160  1450  135  -  9,0 

171  19.0  2.9  2240  1300  135  -27.0 


30 


RADIO  BROADCAST 


MAY,  1928 


EXPERIMENTERS  who  have 
The  Screen-Grid  installed  a  single  screen-grid 
Tube:  Selectivity  tube  ahead  of  a  detector, 
regenerative  or  not,  have  been 
disappointed  at  the  apparent  loss  in  selectivity 
of  the  system,  although  the  gain  increases.  Let 
us  suppose  that  the  resonance  curve  of  a  single- 
stage  of  r.f.  amplification  using  a  201 -A  tube  is 
as  shown  in  Fig.  I .  Now  let  us  use  a  screen-grid 
tube  in  which  the  gain  may  be  twice  as  great. 
In  other  words  every  point  of  the  resonance  curve 
of  Fig.  i  is  boosted  twice  as  high  with  the  result 
as  shown  in  B.  In  any  local  area,  stations  are 
separated  by  50  kc.,  so  that  on  Curve  A  the  in- 
coming signals  from  a  station  50  kc.  off  resonance 
are  below  the  line  which  represents  the  arbitrar- 
ily chosen  signal  magnitude  beyond  which  inter- 
ference occurs.  Now  look  at  Curve  B.  Here  the 
5o-kc.  signal  is  up  out  of  the  area  in  which  no 
interference  occurs,  and  is  heard  in  the  back- 
ground of  the  station  to  which  the  receiver  is 
tuned. 

Let  us  call  the  absolute  selectivity  factor,  the 
ratio  between  the  height  of  the  curve  at  resonance 
to  the  height  at  50  kc.  off  resonance.  This  factor 
for1  curve  A  is  50  •*•  2.4,  or  2.1,  and  for  the  curve 
B  is  100  -t-  4.8,  or  2.1  exactly  the  same.  Then,  if 
the  apparent  selectivity  is  defined  as  the  number 
of  kilocycles  off  resonance  a  signal  must  be  be- 
fore it  is  reduced  to  the  non-interfering  region, 
we  see  that  for  the  201 -A  example  it  is  50  kc. 
while  for  the  Curve  B  where  the  gain  is  twice  as 
great  the  frequency  is  70  kc.  These  figures  de- 
pend, of  course,  upon  the  shape  of  the  resonance 
curve. 

Each  additional  stage  of  201 -A  r.f.  amplifica- 
tion increases  the  gain  of  the  receiver  and  in- 
creases the  selectivity,  but  as  Professor  Hazeltine 
has  shown  in  his  recent  patent,  No.  I,  648,  808 — 
(Nov.  8,  1927) — by  properly  designing  the  inter- 
stage transformers  in  such  amplifiers,  an  increase 
in  selectivity  of  50  per  cent,  can  be  obtained  at  a 
loss  of  only  20  per  cent,  in  amplification.  In 
other  words,  in  a  system  using  successive  tuned 
stages,  relying  upon  resonance  curves  for  selec- 
tivity, there  must  always  be  a  compromise  be- 
tween gain  and  selectivity.  Increasing  the  gain 
without  increasing  the  absolute  selectivity  'at 
the  same  time,  reduces  the  apparent  selectivity. 
Although  the  signal  to  which  the  system  is 
tuned  will  be  louder,  so  will  the  background  pro- 
duced by  other  stations. 

Adding  a  single  stage  of  screen-grid  tube  r.f. 
amplification  under  conditions  which  produce 
maximum  gain  from  that  tube,  decreases  the 
apparent  selectivity  too  much.  Adding  an  extra 
stage,  from  which  we  secure  maximum  amplifica- 
tion, will  boost  the  sensitivity  faster  than  the 
selectivity  is  increased,  and  we  are  no  better  off 
than  before. 

In  other  words,  if  three  stages  of  ZOI-A  am- 
plification are  needed  to  secure  sufficient  selec- 
tivity, more  than  three  stages  will  be  necessary 
when  using  screen-grid  tubes.  This  seems  to  in- 
dicate that  these  tubes  will  not  decrease  the 
number  of  effective  tubes  in  a  receiver,  but  will 
actually  increase  that  number — so  long  as  we 
use  the  t.r.f.  system  of  tuning. 

The  answer,  if  this  reasoning  is  correct,  is  to 
use  a  different  system  of  tuning.  The  super- 
heterodyne is  one  solution;  perhaps  the  Vreeland 
system  described  recently  in  the  I.R.E.  Proceed- 
ings is  another.  This  is  a  system  designed  with 
the  avowed  intention  of  making  a  response  curve 
of  a  receiver  flat  on  top  and  very  steep  on  the 
sides.  It  is  done  by  using  two  closely  coupled 
circuits  so  that  the  resonance  hump  is  not  a 
single  sharp  peak,  but  is  composed  of  two  peaks 
with  a  dip  between.  The  Laboratory  hopes  to 
present  some  quantitive  data  on  this  system 


110 


— Level  above  — 

.which  Signals 

Interfere 


150  100   5C   0   50   100  150  2CO 
KC.  OFF  RESONANCE 

FIG.  I 

soon,  and  in  the  meantime  welcomes  comments 
on  the  problem  outlined  above. 

MANY  TIMES  per  month  we 
Loud  hear  about  some  high  official 

Speaken  in  this  or  that  radio  company 

who  indulges  in  a  bit  of  fore- 
casting, usually  about  the  future  of  radio.  Among 
other  trends,  to  believe  these  officials,  is  that 
toward  greater  power  which  will  be  handled  in  the 
future  radio's  amplifier,  one  executive  going  so  far 
as  to  state  that  our  sets  of  the  future  would  have 
amplifiers  turning  into  our  loud  speakers  at  least 
ten  times  as  much  energy  as  they  do  at  the  pres- 
ent time.  Judging  from  what  has  happened  dur- 
ing the  past  few  years,  one  cannot  doubt  it,  for 
in  the  good  old  days  we  were  satisfied  with  the 
output  of  a  199,  then  we  needed  a  2O1-A  to  deliver 
sufficient  power,  then  the  112,  then  the  171  and 
210  tubes,  and  now  the  250  type.  Each  of  these 
tubes  delivers  considerably  more  power  than  its 
predecessor,  and  to  jump  from  a  j-watt  tube  to  a 
50  waiter  represents  ten  times  as  much  power 
output,  that  is,  10  TU  difference. 

We  are  not  convinced.  Several  years  ago  we 
listened  to  a  pretty  fair  program  coming  from  a 
speaker  that  was  10  TU  better  than  any  speaker 
now  generally  available.  That  is,  it  required  10 
TU  less  power  to  get  a  good  healthy  sound  from 
it.  This  represents  the  difference  between  a  power 
output  of  600  milliwatts  (i7i-A),  and  60  milli- 


Watch  for  the  A.  C.  "Lab"  Receiver 

TTUGH  KNOWLES'  article  describing  the  con- 
L~L  struction  of  the  popular  R.  B.  "Lab"  circuit 
for  a.  c.  operation  will  appear  in  RADIO  BROAD- 
CAST for  June.  The  completed  receiver  has  been 
thoroughly  tested  in  RADIO  BROADCAST  Laboratory 
and  has  proved  very  satisfactory  indeed.  Readers 
will  recall  the  complete  experimental  article  ~.n  our 
April  number  describing  tests  in  the  Laboratory  on 
the  design  of  this  circuit.  The  June  article  describes 
completely  the  construction  of  an  a.  c.  four-tube 
"Lab"  circuit  receiver.  Some  of  its  interesting  fea- 
tures are:  Excellent  efficiency  for  four  tubes:  a.  c. 
operation,  an  extra  socket  and  control  switch  enabl- 
ing quick  transfer  of  the  audio  system  to  phonograph 
pick-up  or  short-wave  tuner  unit,  and  an  interesting 
volume  control. 

— THE  EDITOR 


watts  (2OI-A).  In  other  words,  when  loud  speaker 
manufacturers  are  able  to  build  a  loud  speaker 
with  a  good  characteristic  that  is  10  TU  better 
than  our  present  loud  speakers,  we  can  all  go 
back  to  our  old  2OI-A  tube,  our  B  batteries,  and 
start  all  over  again. 

What  are  the  prospects?  We  have  heard 
that  the  Western  Electric  Company  builds 
a  loud  speaker  much  more  efficient  than  the 
54O-AW,  for  sale  in  England  only.  It  does  not 
have  the  same  tonal  range  as  the  54O-AW  and 
is  cited  only  as  an  example  of  an  efficient 
loud  speaker. 

Incidentally,  present  trends  in  loud  speaker 
design  are  toward  moving-coil  affairs,  elecro- 
dynamic  units,  such  as  the  Magnavox  and  the 
Jensen  cones,  and  the  Vitaphone,  which  is  a 
moving-coil  unit,  coupled  acoustically  to  an 
exponential  horn.  All  of  these  have  very  fine 
frequency  characteristics,  with  honors  at  this 
writing  in  favor  of  the  Jensen.  The  Jensen  is 
made  in  California  and  is  now  generally  available, 
we  understand.  We  have  seen  curves,  above  re-  • 
proach,  which  show  the  Jensen  to  have  a  quite 
flat  response  curve  from  about  60  to  6000  cycles. 
With  a  large  baffle-board,  such  as  obtained  by 
inserting  the  loud  speaker  in  the  walls  of  a  home, 
the  lower  limit  of  response  can  be  pushed  down 
to  about  35  cycles.  A  six-foot  square  baffle  about 
one  and  a  half  inch  thick,  is  however,  very  satis- 
factory. 

If  this  Jensen  unit,  for  example,  could  be  made 
10  TU  more  efficient,  that  is  to  say,  deliver  the 
same  output  with  one-tenth  the  input,  the  result 
would  be  distinctly  worth  achieving.  It  should 
not  be  forgotten,  however,  that  aside  from  the 
question  of  overall  "audio"  efficiency  in  this 
unit,  we  must  supply  the  coil  with  60  mils,  at 
100  volts — 6  watts  of  power. 

The  Magnavox,  too,  is  a  fine  product,  but 
seems  to  suffer  from  excess  filters  which  appear 
to  be  necessary  to  prevent  too  much  a.c.  hum 
from  getting  into  it,  to  cut  down  the  high-pitched 
heterodyne  whistles,  and  other  noises.  In  other 
words,  a  Magnavox  loud  speaker  unit  without  the 
removable  devices  now  employed  to  make  up 
for  our  present  poorly  filtered  a.c.  receivers,  or 
the  present  unfortunate  situation  in  the  ether,  is 
a  fine  unit. 

We  understand  from  an  unimpeachable  au- 
thority that  the  Stromberg-Carlson  engineers 
built  into  stock  receiver  models  a  few  years  ago, 
audio  amplifiers  so  good  that  nearly  all  of  them 
came  back.  Criticism  arose  from  the  fact  that 
these  receivers  seemed  more  noisy  than  sets  of 
other  manufacturers;  more  static  came  in,  and 
"whistles"  were  more  evident.  It  was  a  simple 
matter  at  the  factory  to  put  filters  in  the  amplifier 
system,  cutting  down  on  the  two  ends  of  the 
frequency  spectrum.  Then  the  receivers  stayed 
sold.  It  is  a  fact  that  many  hundreds  of  these 
receivers  have  been  sold  to  Bell  Laboratories 
engineers  and  their  friends.  As  soon  as  they  are 
received  out  comes  the  soldering  iron,  off  comes 
the  filters,  and  out  of  the  loud  speaker  come  the 
low  and  high  frequencies  that  are  so  essential  to 
good  quality. 

IN  THE  article  on  the  four- 
eAn  Error  in  .  tube  "Lab"  receiver  in  the 
Coil  Dimensions  April  RADIO  BROADCAST,  spec- 
ifications were  given  in  Fig.  2 
for  coil  dimensions.  Coils  Li  and  L2  were  shown 
to  consist  of  90  turns,  No.  24  s.c.c.,  on  a  form 
2.5"  in  diameter.  The  correct  designation  should 
have  been  90  turns  No.  24  s.c.c.  on  a  2.0" 
diameter  form.  If  the  reader  already  has  a  2.5" 
coil  form,  he  may  use  66  turns  of  No.  24  s.c.c. 
wire  to  cover  the  same  range. 

— KEITH  HENNEY. 


The  Listeners'  Point  of  View 

HOW  TO  IMPROVE  BROADCASTING 


IN  THE  January  number  we  unburdened  our 
soul  of  some  ingrowing  and  irate  convictions 
in  an  article,  "Are  Radio  Programs  Going  in 
the  Wrong  Direction?"  They  were,  we  said,  and 
the  general  tenor  of  our  hymn  of  complaint  may 
be  recalled  by  quoting:  "Whatever  roseate 
promises  radio  may  have  seemed  to  have  held 
in  the  past,  we  are  at  present  thoroughly  con- 
vinced that  things  have  reached  a  sorry  pass,  and 
that  radio  is  standing  still  —  smug,  self-satisfied, 
and  unutterably  banal.  ...  In  fact  standstill 
is  putting  it  mildly;  the  state  of  affairs  is  more 
exactly  a  retrogression.  All  the  money,  all  the 
ingenuity,  all  the  labor  that  is  being  devoted  to 
the  designing  of  programs  is  being  diligently  de- 
voted to  efforts  in  the  wrong  direction  —  with  the 
result  that  radio  is  going  to  the  dogs  at  a  break- 
neck speed,  so  rapidly,  in  fact,  that  to  check  it 
will  require  no  little  effort." 

During  the  four  months  which  have  elapsed 
since  publishing  this  diatribe  we  have  had  an 
unusual  number  of  communications,  ranging  all 
the  way  from  heartiest  endorsement  to  bitterest 
denunciation. 

One  commentator  says:  "The  writer  is  one  of 
those  humans  who  inordinately  admires  a 
'kicker'  if,  and  when,  said  kicker  registers  his 
kick  with  some  accuracy  and  a  lot  of  eclat.  That 
is  preparatory  to  a  100  per  cent,  endorsement  of 
your  kick  in  the  January  RADIO  BROADCAST — 
'Are  Radio  Programs  Going  in  the  Wrong  Direc- 
tion?' Every  word  in  this  article  is  pregnant  with 
common  sense  and  as  true  as  Gospel."  (Such 
perspicuity!  J.  IV.) 

Another  correspondent  states:  "You  are  just 
like  all  the  rest  of  the  tribe  of  critics — 'smug  and 
self-satisfied."  What  good  do  you  expect  to  effect 
by  such  destructive  criticism  as  is  contained  in 
your  article  in  the  January  RADIO  BROADCAST? 
Here  thousands  of  people  throughout  the  coun- 
try have  been  putting  in  eight  hours  a  day  for 
the  last  five  years  to  make  radio  what  it  is  to- 
day and  then  you  come  along  and  in  an  article 
that  couldn't  have  taken  two  hours  to  write, 
presume  to  set  at  naught  all  this  accomplish- 
ment." (O  my,  O  my,  it  sometimes  takes  us 
twenty  hours  to  write  one  of  these!  J.  IP.) 

Such  was  the  run  of  lay  comment.  We  quote 
two  other  replies,  both  from  members  of  "the 
profession."  These  retorts  were  not  addressed 
directly  to  us  but  were  forwarded  to  "Pioneer" 
of  the  New  York  Herald-Tribune  who  quoted 
our  unkind  remarks  in  his  column.  One  is  from 
the  president  of  two  small  stations  and  the 
other  from  the  president  of  the  National  Broad- 
casting Company.  Mr.  Donald  Flamm,  president 
of  stations  WMCA  and  WPCH,  in  a  lengthy  open 
letter  said,  among  other  things: 

"It  is  to  answer  Mr.  Wallace,  as  well  as  the 
radio  critic  through  whose  courtesy  Mr.  Wal- 
lace's remarks  were  presented,  that  this  is  writ- 
ten. 1  don't  propose  to  speak  for  all  the  broad- 
casters. 1  am  simply  giving  my  own  opinion, 
based  upon  three  years  of  association  with  the 
radio  industry  and  particularly  with  the  broad- 
casting end  of  the  business.  ...  I,  too,  have  come 
to  the  realization  that  radio  is  at  a  standstill 
and  ...  it  is  not  within  the  province  of  the  radio 
impresario  to  do  very  much  about  it.  And,  fur- 
thermore, it  is  going  to  remain  at  a  standstill 
unless  some  very  remarkable  change  occurs  in 
the  very  art  of  radio  broadcasting  itself— a 


By  JOHN  WALLACE 

change  that  is  entirely  beyond  our  control. 
.  .  .  Let  us  consider  .  .  .  the  plight  of  the  broad- 
caster. 

"He  can  appeal  to  his  audience  only  through 
sound — nothing  else.  .  .  .  There  is  nothing  in  the 
world  he  can  add  to  his  'tools'  with  which  to  ac- 
complish so-called  showmanship.  There  is  an- 
other angle  that  we  cannot  overlook  .  .  .  the  fact 
that  the  broadcaster  is  constantly  doing  some- 
thing different.  In  writing  a  play,  the  author 
takes  weeks  and  sometimes  months  .  .  .  the  stage 
director  continues  the  job  and  shapes  and 
changes  the  play  .  .  .  until  it  is  finally  ready  for  a 
long,  or  perhaps  a  short,  run  on  Broadway. 
The  same  play  is  repeated  performance  after 
performance  without  the  slightest  variation  of 
a  line  or  a  movement.  The  author's  job  is  done, 
the  director's  job  is  done,  the  producer's  job  is 
done.  How  different  is  the  task  of  the  broad- 
caster! Every  program  must  be  different.  And 
as  in  the  case  of  WMCA,  which  goes  on  the  air 
at  9  o'clock  each  morning  and  continues  broad- 
casting right  through  the  day  and  evening  until 
sometimes  as  late  as  2  A.  M.,  what  opportunity 
have  we  for  observing  these  rules  of  'showman- 
ship'? 

"After  all,  what  is  there  that  we  can  present 
to  the  public  that  will  display  good  'showman- 
ship' and  'intelligence'?  Radio  impresarios 
have  presented  almost  every  great  living  artist 
available.  There  is  not  a  musical  organization 
in  the  country  whose  services  have  not  been 
utilized  at  some  time  or  other.  During  the  course 
of  the  year  we  have  also  presented  hundreds  of 
orchestras,  numerous  celebrities  from  all  walks 
of  life,  interesting  and  informative  talks  by 
competent  authorities,  vaudeville  programs, 
short  programs  and  long  programs;  in  short, 
we  have  availed  ourselves  of  every  possible  form 
of  entertainment.  We  have  not  left  a  stone  un- 
turned in  our  effort  to  bring  to  our  audience  the 
complete  range  of  program  material.  Beyond 
that  we  can  do  no  more." 

Mr.  M.  H.  Aylesworth,  president  of  the  Na- 
tional Broadcasting  Company  said,  in  part: 

"I  have  read  with  considerable  interest  the 
various  criticisms  of  broadcasting  programs 
.  .  .  which  you  recently  quoted  in  your  interesting 
column.  It  has  occurred  to  me  that  a  short  re- 
sume of  the  talent  which  has  been  made  available 
through  the  system  of  the  National  Broadcasting 
Company  and  associated  stations  by  American 
industries  who  are  sponsoring  national  programs, 
as  well  as  those  produced  by  the  National 
Broadcasting  Company,  and  associated  stations 
in  the  last  sixty  days  (January  and  December), 
shows  something  of  the  vast  undertaking  in 
arrangement  and  finance  to  make  possible  the 
feasible  reception  of  these  speakers  and  artists 
by  the  American  radio  public."  The  resume, 
which  is  entitled  "A  Partial  List  of  Outstanding 
Broadcasts  by  the  National  Broadcasting  Com- 
pany," is  given  herewith: 

Artists,  actors,  and  actresses — Ernest  Hutche- 
son,  Percy  Grainger,  Ohman  and  Arden,  Irene 
Scharrer,  Ethel  Leginska,  Robert  Armbruster, 
Ignace  Friedman,  Herbert  Carrick,  George 
Gershwin,  Josef  Lhevinne,  Adam  Carroll, 
Richard  Rodgers,  J.  Milton  Del  Camp,  Richard 
Buhlig,  Benno  Moiseiwitsch,  and  Mme.  Wanda 
Landowska,  pianists;  Mischa  Weisbord,  Paul 

3' 


Kochanski,  and  Arcadie  Birkenholz,  violinists; 
Ethel  Hayden,  Van  and  Schenck,  Katherine 
Meisle,  Editha  Fleischer,  Reinald  Werrenrath, 
Maria  Kurenko,  Marie  Tiffany,  Elsie  Baker, 
Arthur  Hacket-Granville,  William  Simmons, 
Mary  Lewis,  Armand  Tokatyan,  Ann  Mack, 
Mary  Garden,  Al  Jolson,  John  Charles  Thomas, 
Emilio  de  Gorgoza,  Merle  Alcock,  Mario  Cham- 
lee,  Duncan  Sisters,  Tita  Ruffo,  Fanny  Brice, 
Claudia  Muzio,  Cliff  Edwards,  Rosa  Ponselle, 
Giovanni  Martinelli,  Ezio  Pinza,  Richard 
Crooks,  and  So'phie  Braslau,  singers;  "Chick" 
Sale,  Joe  Cook,  Dr.  Rockwell,  Fred  and  Dorothy 
Stone,  Leo  Carilla,  Weber  and  Fields,  and 
Cornelia  Otis  Skinner,  actors. 

Orchestras  and  orchestra  leaders — Walter  Dam- 
rosch,  conducting  the  New  York  Symphony  Or- 
chestra; Fritz  Busch,  guest  conductor;  Roderic 
Graham,  conducting  G.  M.  Symphony  Orches- 
tra; Patrick  Conway  and  band,  Edwin  Franko 
Goldman  and  band,  Paul  Whiteman  and  or- 
chestra, Vincent  Lopez  and  orchestra,  and  Ben 
Bernie  and  orchestra. 

Authors  and  explorers — Robert  Benchley, 
Will  Rogers,  Irvin  S.  Cobb,  Ford  Madox  Ford, 
Louis  Golding,  Glenway  Westcott,  Louis  Brom- 
field,  Commander  George  Dyott,  Fannie  Hurst, 
Helen  Hull,  Elmer  Davis,  Cosmo  Hamilton, 
S.  S.  Van  Dine,  Dr.  Ralph  Sockman,  John  B. 
Kennedy,  Homer  Croy,  Grantland  Rice,  and 
Bruce  Barton. 

ARGUMENTS  FOR  THE  DEFENSE 

IN  VI EW  of  the  foregoing  we  have  a  defense  of 
our  January  remarks,  and  an  enlargement  of 
them. 

To  those  who  objected  that  our  stand  was  de- 
structive, our  retort  is:  It  wasn't.  We  claim, 
constructively,  that  serious  instrumental  music 
should  be  the  backbone  of  radio  entertainment. 
We  offered  no  constructive  suggestions  as  to 
what  should  make  up  the  balance  of  programs, 
not  because  we  had  no  ideas  on  the  subject  but 
simply  because  of  lack  of  space.  Specific  ideas 
along  those  lines  follow. 

As  for  Mr.  Aylesworth's  reply — sorry,  but 
we're  going  to  quote  again  from  the  January 
squawk:  "What  is  the  right  direction  for  pro- 
gram making  to  take?  Program  makers  are  too 
embroiled  in  their  business  to  glance  at  the  guide- 
posts,  too  pressed  by  the  strenuous  and  unceas- 
ing job  of  making  programs  to  take  a  moment 
or  two  off  for  a  little  rational  reflection  on  what 
their  job  is  all  about.  They  persist  in  refusing  to 
take  account  of  the  fact  that  radio  is  a  new 
medium,  a  unique  medium  and,  like  any  other 
medium,  endowed  with  its  peculiar  limitations 
and  peculiar  possibilities.  Pig-headedly,  they 
persist  in  attempting  to  reconcile  with  their 
duties  the  traditions  of  the  drama,  the  opera, 
the  music  hall,  and  the  vaudeville  stage." 

In  view  of  these  remarks  Mr.  Aylesworth's  re- 
buttal is  seen  to  contain  its  own  refutation.  All 
the  individuals  he  mentions  are  recruited  from 
"the  drama,  the  opera,  the  music  hall,  and  the 
concert  stage."  However,  we  will  not  gloat  over 
Mr.  Aylesworth's  self-confounding;  our  victory 
is  merely  a  dialectic  one.  For  the  fact  is  that  the 
programs  he  mentions  are  the  very  best  that 
are  at  present  discoverable  on  the  air. 

But  it  is  unfortunate  that  this  is  true  for  such 
programs  represent  not  progress,  but  stand- 


32 


RADIO  BROADCAST 


MAY,  1928 


still.  They  are  good  in  their  way,  but  they  re- 
main a  makeshift,  a  borrowing.  Multiplying 
them  to  the  w'th  degree  would  still  be  doing 
nothing  to  serve  the  ultimate  ends  of  radio  as 
a  permanent  institution.  Radio  must  develop 
its  own  artists,  actors,  actresses,  and  orchestras. 
These  may  also  do  work  in  the  other  field  but 
they  must  be  first  of  all  radio  performers.  What 
Mr.  Aylesworth  lists  is  not  radio  performers 
but  names  names,  names. 

Mr.  Flamm,  quoted  above,  agrees  with  us — 
but — we  do  not  agree  with  him.  Our  version  of 
the  predicament  was  not  pessimistic.  His  is.  We 
claimed  that  nothing  was  being  done  to  get 
radio  out  of  its  rut.  He  claims  that  nothing  can 
be  done. 

THE  BROADCASTER  CAN'T  IMPROVE  BROADCASTING 

THERE  the  broadcaster — if  Mr.  Flamm  can 
be  taken  as  representative — lays  all  his 
cards  on  the  table  and  discloses  himself  for  what 
he  is — an  unimaginative  soul  who  isn't  fitted  to 
guide  his  own  destinies.  He  laments  that  the 
broadcaster  can  appeal  only  through  sound.  He 
should  rejoice.  Sound.  There  is  his  medium — 
plainly  and  unmistakably  identified.  There  are 
half  a  million  sounds  in  existence  awaiting  his 
use  of  them.  Obdurately  he  ignores  them.  The 
conclusion  toward  which  we  have  been  labor- 
ing should  by  now  have  made  itself  manifest: 
the  broadcaster  can't  improve  broadcasting. 

If  broadcasting  is  to  be  extricated  from  the 
rut  of  dull  routine  in  which  it  finds  itself,  it  is  evi- 
dent that  the  help  must  come  from  without. 

Why?  The  reason  is  plain  enough.  The  broad- 
caster is  first  of  all  a  business  man — an  impre- 
sario. If  he  transcends  that  he  may,  in  some 
instances,  be  also  an  interpretative  artist.  But 
by  no  stretching  of  the  imagination  can  he  be 
regarded  as  a  creative  artist.  Nor  are  the  gents 
on  his  staff  of  continuity  writers  likely  to  be 
creative  artists.  Creative  artists  are  rare  birds 
and  not  likely  to  be  found  among  the  hirelings  of 
a  big  industry.  The  result  is  that  nothing  is 
being  created  for  radio;  without  creation  no 
art  can  come  into  being — including  radio  art. 

True,  there  are  program  makers  who  go 
through  some  of  the  motions  of  creating.  But 
they  haven't  got  the  goods  in  them  and  what 
finally  results  is  merely  a  banal,  or  at  best 
"tricky"  arrangement  of  a  lot  of  old  stuff. 

The  broadcasters,  however,  have  no  occasion 
to  resent  this  indictment  of  their  artistry.  We 
wouldn't  have  them  artists!  Imagine  what 
would  happen  to  the  National  Broadcasting 
Company  if  a  crew  of  long  haired  birds  should 
try  to  run  it.  It  would  go  out  of  business  in  three 
days.  The  broadcasters  are  marvels  of  efficiency 
in  their  own  field.  They  have  effected  the  most 
rapid  growth  that  any  industry  has  ever  known. 
All  honor  is  due  them.  The  only  trouble  is  that 
they  are  trying  to  extend  their  field  outside  of 
its  legitimate  limits.  Impresarios,  well  and 
good;  but  creators — phooey! 

Now  the  truth  of  the  matter  is  that  there  is 
an  Art  of  Broadcasting.  The  only  trouble  is  that 
it  hasn't  been  discovered  yet.  There  have  been 
inklings  and  foreshadowings  of  what  it  is  to  be. 
But  these  foreshadowinps,  though  they're  as 
obvious  as  the  nose  on  your  face,  have  been  prac- 
tically ignored.  To  mention  a  couple  of  these 
harbingers,  one  was  the  Eveready  Hour's 
"Galapagos"  and  the  other  was  that  same  or- 
ganization's "Show  Boat." 

These  two  programs  came  at  least  nearer  than 
any  others  to  demonstrating  what  the  new  radio 
art  form  will  be  like.  But  excellent  as  they  were 
they  only  faintly  suggest  the  unexplored  possi- 
bilities of  what  we  hereby  dub  "Sound  Drama." 

We  don't  propose  to  write  you  a  "Sound 
Drama."  In  the  first  place  that's  not  what 


we're  hired  to  do,  and  in  the  second  place  we 
haven't  the  necessary  talents  to  do  it.  But  it  is 
within  our  rights  and  powers  to  prophesy  what 
the  so  far  unwritten  "Sound  Drama"  will  be 
like.  It  will  be  a  little  like  the  Stage  Drama.  It 
will  be  a  little  like  the  Opera.  It  will  be  a  little 
like  the  Symphony.  It  will  be  a  little  like  Liter- 
ature. It  will  be  a  little  like  the  Oratorio.  And  it 
will  be  exactly  like  no  one  of  these.  What  it  will 
be  is  the  perfect  synthesis  of  all  the  modes  we 
have  mentioned.  Which  also  means  it  will  be 
quite  a  chore  in  the  making!  No  ordinary  ham 
is  going  to  be  able  to  take  all  these  art  forms 
and  weld  them  into  a  whole  which  will  be  not 
merely  a  conglomeration  but  a  unity,  an  art 
form  in  itself.  It  is  a  task  for  a  creative  artist  of 
the  highest  ability  and  originality.  The  artist 
who  does  it  will  have  to  be  Playwright,  Com- 
poser, and  Poet  all  at  once — in  other  words 
such  a  man  as  was  Richard  Wagner.  He  need  not 
be  technically  equipped  in  each  one  of  these 
fields  of  art.  But  his  taste,  at  least,  must  direct 
the  efforts  of  collaborators  to  a  unified  end.  (It 
is  needless  to  add  that  he  must  also  familiarize 
himse'lf  with  the  mechanical  limitations  of  radio 
transmission  and  adapt  his  music  and  all  else 
he  offers  to  these  requirements.) 

The  time  is  now  ripe  for  the  new  art  to  appear, 
for  the  radio  lords  have  brought  radio  up  to  the 
point  where  it  is  susceptible  of  being  made  an 
art.  To  their  credit  it  must  be  said  that  radio 
is  miles  ahead  of  the  writing  that  is  being  done 
for  it.  Radio  technicians  have  done  astounding 
things.  They  have  developed  their  apparatus 
and  their  knowledge  of  transmission  to  the  point 
where  they  can  do  wonders.  But  there  are  no 
wonders  to  be  done.  Most  of  the  truck  that  is 
on  the  air  is  an  insult  to  the  excellence  of  the 
apparatus  that  transmits  it. 

Radio  play  directors  have  made  exhaustive 
researches  in  the  realm  of  noises.  They  have 
learned  how  properly  to  imitate  hundreds  of 
noises  in  nature.  But  so  far  they  have  been  un- 
able to  put  these  noises  to  any  artistic  use. 
.  The  radio  engineers  and  the  studio  staffs 
have  done  their  share.  They  have  set  the  stage. 
What  they  need  now  is  something  worth  while  to 
put  on  that  stage.  And  they  ought  to  realize 
that  they  can't  produce  it.  They  must  call  for 
outside  help.  Their  position  is  much  like  that 
of  an  expert  violin  maker  who  has  put  in  months 
of  loving  craftsmanship  in  the  making  of  a  per- 
fect instrument.  This  same  craftsman  doesn't 
attempt  to  perform  on  the  fiddle  when  it  is 
finished.  He  leaves  that  to  the  artist. 

So  the  radio  program  makers  must  sooner  or 
later  summon  the  aid  of  the  artist.  An  artist  is 
attracted  to  a  new  medium  by  four  different 
factors:  ;.  The  artistic  possibilities  of  the 
new  medium.  2.  The  possibilities  of  reaching  an 
appreciative  audience  through  that  medium. 
3.  The  permanence  of  the  medium.  And,  4.  The 
rewards  available  in  that  medium. 

That  radio  has  artistic  possibilities  we  are 
firmly  convinced.  That  radio  has  a  large  and 
sympathetic  audience  is  an  obvious  fact.  That 
the  medium  is  at  present  a  most  ephemeral  one 
happens  also  to  be  a  fact,  but  one  of  no  per- 
manent importance.  Now,  a  program  is  given 
once  and  forgotten  sixty  minutes  later.  Which 
is  generally  what  it  deserves.  But  there  is  no 
reason  why  a  radio  creation  of  sufficient  merit 
and  meaty  content  could  not  be  given  again 
and  again  and  find  a  permanent  place  on  the  rep- 
ertoires of  stations  throughout  the  world. 

As  to  the  rewards  available  for  creative  radio 
program  designing,  that  brings  us  up  against  the 
practical.  At  present  there  is  no  financial  in- 
ducement for  any  one  to  worry  his  head  over  the 
future  of  radio — unless  he  be  a  paid  "contin- 
uity" writer,  in  which  case  he  does  just  enough 


worrying  to  earn  his  salary.  Many  millions  of 
dollars  are  spent  in  this  country  every  year  on 
radio  programs.  It  is  our  conjecture  that  of  these 
many  millions  of  dollars  less  than  a  tenth  of  one 
per  cent,  goes  to  paying  for  the  writing  of  broad- 
cast programs.  Much  of  it  is  wasted  on  paying 
the  extravagant  bills  of  opera  singers  and  other 
overpaid  interpretative  artists. 

If  less  money  were  lavished  on  the  individuals 
who  interpret  things,  and  more  money  spent  in 
getting  them  something  to  interpret,  matters 
would  be  vastly  improved. 

As  a  practical  suggestion  of  a  method  to  start 
the  ball  rolling,  we  propose  the  following: 

Let  some  station  or  syndicate  of  stations  post 
a  prize  of  §5000  for  the  best  specially  composed 
program  of  sixty  minutes  duration  submitted 
in  manuscript  by  October  I,  1928.  The  privilege 
of  purchasing  other  compositions  at  more  ordi- 
nary rates  could  be  reserved  by  the  station  offer- 
ing the  prize.  Certain  copyright  stipulations 
would  also  have  to  be  arranged. 

What  will  this  winning  composition  be  like? 
We  will  suggest  its  make-up.  It  will  be  a  collab- 
oration between  a  modern  composer — a  Hon- 
neger,  say — and  a  writer  or  poet.  The  announcer 
will  introduce  it  with  not  more  than  two  or  three 
minutes  of  explanatory  foreword.  He  will  not 
intrude  again.  This  imagined  program  will  open, 
say,  with  a  vague  rumble  of  distant  noises.  They 
will  steadily  grow  louder  and  presently  organ- 
ize themselves  out  of  the  chaos  into  recogniz- 
able sounds.  They  will  be  the  noises  of  nature, 
perhaps  the  beating  of  surf,  the  noise  of  a  street, 
or  the  buzzing  of  insects.  They  will  constitute 
the  setting.  But  these  noises  will  be  craftily 
selected,  manipulated,  minimized,  or  exag- 
gerated. Some  may  be  amplified  to  a  high  degree 
— as  they  would  sound,  for  instance,  to  the  keen 
ears  of  a  wild  animal.  They  will  suggest  the 
mood  of  the  entire  piece. 

Imperceptibly  they  will  melt  into  music,  the 
music  of  the  symphony  orchestra,  which  will 
continue  to  build  up  the  mood.  Then  the  music 
will  grow  quieter,  a  modulation  will  change  its 
key  and  its  tempo  until  presently  it  will  merge, 
without  any  break,  into  the  human  voice.  Not 
your  ordinary  human  voice,  but  the  voice  of  an 
artist  actor  which  can  convey  the  slightest 
nuance  of  emotion.  And  the  words  will  not  merely 
be  words,  but  just  the  right  words.  They  will 
be  as  informative  as  the  words  in  any  stage 
play,  but  at  the  same  time  they  will  be  prose 
poetry.  They  will  further  clarify  the  situation, 
or  plot,  which  will  of  necessity  be  an  elemental 
and  emotional  one.  The  speaker's  words  may  at 
any  time  change  into  song  and  perhaps  back 
again.  Presently  the  noises  will  be  heard  again,  or 
the  orchestra,  or  perhaps  a  chorus  of  voices — 
observers  commenting  on  what  transpires.  And 
so  on,  all  these  various  sound  sources  will  be  man- 
ipulated and  shuttled  about  until  the  comedy 
or  the  melodrama,  the  tragedy  or  fantasy,  what- 
ever it  is,  has  come  to  a  close. 

In  thus  briefly  setting  down  our  ideas  of  the 
possible  trend  of  such  a  Sound  Drama,  we  have 
perhaps  made  the  thing  seem  simply  curious  and 
"tricky."  Perhaps  we  have  made  it  seem 
"highbrow."  If  it  is  properly  composed  and  ex- 
ecuted it  will  be  none  of  these.  It  will  be  a  grip- 
ping emotional  thing  that  will  completely  carry 
us  away.  It  will  not  be  something  vague  and  dis- 
jointed that  we  will  forget  immediately  it  is 
over,  but  something  rememberable  and  pleas- 
urable. And  it  will  have  accomplished  its  end, 
not  through  visible  means,  nor  verbal  descrip- 
tion, but  through  an  appeal  to  that  much 
neglected  organ  of  ours — the  ear. 

And  still  the  broadcaster  laments  that  he 
"can  appeal  to  his  audience  only  through  sound 
— nothing  else!" 


"Our  Readers  Suggest 


OUR  Readers  Suggest.  .  ."  is  a  regular  feature 
of  RADIO  BROADCAST,  made  up  of  contri- 
butions from  our  readers  dealing  with  their  experi- 
ences in  the  use  of  radio  apparatus.  Little  "kinks," 
the  result  of  experience,  which  five  improved  oper- 
ation, will  be  described  here.  Regular  space  rates  will 
be  paid  for  contributions  accepted,  and  these  should 
be  addressed  to  "Our  Readers  Suggest  Editor," 
RADIO  BROADCAST,  Garden  City,  New  York. 

— THE  EDITOR 


Remote  Volume  Control 

THE  operation  of  a  receiver  by  remote 
control  is  an  interesting  possibility,  and 
one  that  has  intrigued  many  engineering 
minds.  The  mechanical  and  electrical  complica- 
tions of  existing  systems  are  such,  however,  as 
to  preclude  their  general  use.  It  is,  nevertheless, 
a  relatively  simple  matter  to  control  the  volume 
of  a  receiver  from  your  easy  chair,  which,  though 
only  partially  solving  the  problem,  is  really  a 
great  convenience.  The  radio  fan  is,  I  think, 
inherently  a  lazy  individual.  Writing  from  per- 
sonal experience  I  may  say  that  there  is  nothing 
more  annoying  than  finding  it  necessary  to 
rise  from  a  comfortable  chair  or  sofa  to  tone 
down  or  bring  up  volume  on  a  receiver  that  a 
few  minutes  before  was  apparently  correctly  ad- 
justed. 

Fans  indisposed  to  labor  have  undoubtedly 
noted  that  the  volume  of  a  receiver  is  anything 
but  constant.  An  original  adjustment  made 
when  the  broadcaster  was  using  the  soft  pedal, 
proves  entirely  off  on  a  fortissimo  passage.  Also, 
in  congested  radio  districts,  the  intensity  of 
signals,  I  have  found,  varies  considerably  with 
the  number  of  receivers  tuned  to  the  same  pro- 
gram in  the  immediate  neighborhood.  This  is  not 
due  to  an  absorption  effect  upon  the  field 
strength,  but  rather  to  a  parallel  wave  trap 
effect.  Regardless  of  the  reason,  the  condition 
exists  and  can  be  made  more  tolerable  by  provid- 
ing a  means  of  volume  control  from  wherever 
the  indolent  listener  may  be  reclining. 

The  writer  uses  a  variable  zero  to  five-thou- 
sand ohm  resistor  connected  between  the 
antenna  and  ground  posts  of  the  receiver  by 
means  of  a  long  flexible  telephone  cord.  This  is 
employed  as  an  auxiliary  volume  control  to  the 
adjustment  provided  on  the  receiver  itself.  The 
original  volume  control  is  set  for  a  degree  of 


vqlume  quite  a  bit  in  excess  of  comfortable 
listening,  and  is  toned  down  by  the  external 
control. 

I   have  found   that  practically  any  variable 
resistor,  covering  a  range  of  from  five  to  at  least 
five-hundred  ohms,  is  satisfactory  for  the  pur- 
pose   described.    It    is    apparently    immaterial 
whether  or  not  the  resistor  is  inductive. 
JAMES  MONTAGUE, 
Newark,  New  Jersey. 

STAFF   COMMENT 

CLECTRAD,  Clarostat,  Yaxley  and  others  are 
*-*  manufacturing  remote  volume  controls  of 
the  type  described  by  our  contributor.  Their  use 
in  the  antenna  circuit,  where,  of  course,  signal 


A   NEW   CLAROSTAT 

It  is  the  remote  vo'ume  control  type.  Elec- 
trad  Yaxley  and  others  have  similar  controls 

intensity  is  reduced  before  the  signal  is  impressed 
on  the  audio-frequency  circuits,  precludes  the 
possibility  of  overloading,  with  resulting  dis- 
tortion. 

Devices  of  this  nature  can  be  made  to  serve  a 
utilitarian  purpose  other  than  Mr.  Montague's 
commendable  moral  support  to  laziness.  Such  a 
volume  control  installed  near  the  telephone  is  a 
logical  arrangement  of  genuine  utility,  and  will 
be  greatly  appreciated  by  persons  who  have 
endeavored  to  converse  over  the  'phone  in  com- 
petition with  the  radio. 

Improving  Your  B  Device 

CEVERAL  articles  have  appeared  in  "Our 
^  Readers  Suggest"  department  on  the  im- 
provement of  socket  power  devices.  These 


articles  have  considered,  singly,  the  stabilizing 
possibility  of  the  glow  tube,  the  use  of  additional 
resistors  to  obtain  desired  plate  potentials,  and 
the  use  of  C  biasing  resistors.  It  is  the  purpose  of 
this  article  to  describe  a  simple  arrangement 
which  takes  care  in  one  unit  of  these  various 
desirable  possibilities. 

The  starting  point  in  improving  the  existing 
B  device  is  in  the  rectifier  tube.  In  this  connec- 
tion it  is  necessary  first  to  clarify  a  misunder- 
standing which  has  gained  ground  of  late, 
namely,  that  a  rectifier  tube,  when  renewed, 
must  be  replaced  bv  one  of  identically  the  same 
type. 

With  virtually  any  good  Raytheon  B  socket 
power  outfit  heretofore  provided  with  the  Ray- 
theon B  type  rectifier,  an  increase  in  voltage  out- 
put may  be  obtained  by  substituting  the  present 
Raytheon  type  BH  tube  for  the  old  B  type.  The 
voltage,  providing  it  was  adequate  for  the  re- 
quirements of  the  output  tube  used  before  this 
substitution,  now  is  of  sufficient  value  to  take 
care  of  the  grid  biasing  requirements  of  the 
power  tube  as  well  as  its  plate  supply  demands. 

Other  improvements  for  B  devices  have  taken 
the  form  of  better  voltage  regulation  at  the 
output  end.  Reliable  potentiometer  resistances, 
together  with  a  voltage  regulator  tube,  will 
maintain  fixed  voltages  across  two  or  more 
terminals. 

The  photographs  on  page  34  present  an 
adapter  which  may  be  connected  to  many  of  the 
better  quality  B  power  units  so  as  to  incorporate 
the  advantages  of  a  potentiometer  resistance  net- 
work and  a  regulator  tube,  while  increased 
voltage  output  is  obtained  for  use  as  grid  bias 
by  replacing  the  B  type  with  the  BH  type  Ray- 
theon, as  mentioned  above.  It  will  be  noted  from 
Fig.  2  that  the  adapter  comprises  a  tapped  po- 
tentiometer resistance,  two  bypass  condensers,  a 
socket  for  the  R  (regulator)  tube,  and  a  special 
current-limiting  resistor  for  use  in  the  third 
element  circuit  of  the  regulator  tube.  These  few 
parts,  along  with  the  necessary  binding  posts, 
may  be  mounted  in  almos,t  any  desirable  manner. 

Fig.  I  shows  a  typical  B  unit  circuit,  with  the 
original  resistors  supplying  the  potential  re- 
quirements of  last  year's  receivers.  Fig.  21  shows 
a'wiring  diagram  of  the  additional  unit  described 
by  the  author.  Point  "A"  is  connected  to  point 
"A"  in  Fig.  I  and  point  "B"  to  point  "B"  in 
Fig.  I.  The  center  choke  tap  runs  through  the 


Raytheon 


OBtMax. 


OBtlst.A.F< 


oc- 


FIG. 


FIG.    2 


33 


34 


oooo-ohm  resistor  to  the  metallic  base  of  the 
regulator  tube  from  "X"  i'n  Fig.  2!  to  "X"  in 
Fig.  i. 

The  following  table  shows  the  value  of  the 
resistors  designated  in  Fig.  2: 

RI  looo  ohms,  5  watts 
R-2  2000  ohms,  5  watts 
R3  50000  ohms,  2  watts 
R<  20000  ohms,  2  watts 
Rs  9000  ohms,  5  watts 

R6  2000  ohms,  (double   potentiometer,    such 
the  Amsco  "duostat") 


as 


The  constructor  should  find  no  difficulty  in 
following  the  layout  of  parts  by  reference  to  the 
photographs. 

D.  E.  REPLOOLE, 
Cambridge,  Massachusetts. 

STAFF    COMMENT 

THE  arrangement  shown  in  Fig.  2  may  be 
used  with  practically  any  socket  power 
device.  As  was  pointed  out  in  previous  articles 
of  this  nature  in  "Our  Readers  Suggest"  Depart- 
ment, however,  the  C  bias  arrangement  should 
be  employed  only  with  a  socket  power  unit 
capable  of  delivering  a  total  voltage  output 
under  load  equalling  the  sum  of  the  maximum 
plate  and  grid  voltage  required.  The  grid  bias 
feature  may  be  eliminated  by  the  omission  of  €2 
and  R6  and  by  the  connection  of  the  bottom  of 
R4  to  the  regulator  tube  and  to  "B"  on  the 
regular  B  device.  This  connection  is  indicated  in 
dotted  lines,  the  heavy  line  being,  of  course, 
left  out 

Plate  Detection 

THE  advantages  of  using  a  C  battery  for  bias 
in  the  detector  circuit  may  be  retained 
without  the  use  of  an  extra  battery  by  a  simple 
change  in  the  wiring  of  any  circuit.  In  the 
writer's  case  a  resistance-coupled  audio  amplifier 
is  used  for  the  first  stage.  The  detector  grid 
condenser  and  leak  are  no  longer  used,  and  are 
"shorted"  out  of  the  circuit. 

Connect  the  detector  rheostat  in  the  A  minus 
filament  line  and  connect  the  grid  return  as 
shown  in  Fig.  3,  which  arrangement  utilizes  the 
negative  bias  obtained  by  the  drop  across  the 
filament  rheostat.  A  definite  value  of  resistance 
in  the  detector  plate  circuit  will  be  found  to 
work  best  with  each  value  of  C  bias.  In  this 
case  a  one-megohm  leak  was  found  to  be  right 
when  ninety  volts  was  used  with  a  2OI-A  type 
tube. 

This  arrangement  was  found  to  be  practically 
as  sensitive  as  the  usual  circuit  having  a  grid 
leak  and  condenser,  and  at  the  same  time  had 


Detector 


Ist.A.F. 


RADIO  BROADCAST 


This  adapter,  des- 
cribedbyMr.  Replogle, 
modernises  the  old  B 
supply  device.  A  glow 
tube  is  used 


the  selectivity  and  tone  qualities  gained  by 
employing  plate  detection. 

KARL  V.  NYQUIST, 
Stromsbing,  Nebraska. 

STAFF   COMMENT 

p\ETECTING  on  the  lower  bend  of  the 
'--'  plate-current  grid  potential  characteristic 
curve,  like  most  justifiable  variations  from  an 
average  procedure,  is  characterized  both  by  ad- 
vantages and  disadvantages.  The  possibility 
of  distortion  due  to  overloading  of  the  detector 
circuit  is  reduced  in  the  so-called  plate  method  of 


MAY,  1928 

speaker  can  handle  without  distortion.  The 
correct  adjustment  can  be  easily  made  with  the 
aid  of  such  simple  apparatus  as  is  generally 
found  in  the  radio  equipped  home. 

A  no-volt  lamp  of  indiscriminate  wattage, 
a  house  current  plug,  and  a  looo-ohm  resistor  are 
required  to  make  the  adjustment.  This  apparatus 
is  placed  in  series  with  no  volts  a.  c.  and  the 
loud  speaker.  The  set  screw  on  the  loud  speaker 
collar  is  loosened  and  the  circuit  shown  in  Fig.  4 
is  closed.  A  I2o-cycle  hum  will  be  distinctly 
heard  in  the  loud  speaker.  The  screws  holding 
the  frame  should  be  loosened  slightly  and  the 
actuating  mechanism  moved  from  side  to  side 
and  up  and  down  until  the  sound  is  at  a  mini- 
mum. With  the  set  screw  loosened  the  loud 
speaker  will  rattle  freely  at  this  adjustment. 
The  current  is  turned  off  and  the  set  screw  is 
tightened  down  upon  the  pin. 

HARRY  WIRTH, 
New  York  City. 

Selectivity  with  A.  C.  Tubes 

LJAVING  had  occasion  to  alter  a  half  dozen 
*  or  so  battery  receivers  for  a.  c.  operation, 
with  both  the  R.  C.  A.  and  Arcturus  types  of 
tube,  I  have  noticed  that  the  selectivity  of  the 
battery  receiver  has  been,  in  every  case,  notice- 
ably superior  to  that  of  the  rewired  job.  In  the 
course  of  my  experiments,  however,  I  found 
that  the  selectivity  of  the  a.  c.  set  could  be  im- 
proved until  it  was  quite  on  a  par  with  the 
original  201 -A  job,  by 
increasing  the  negative 
bias  on  the  r.  f.  tubes. 
WALTER  BENNETT, 
New  York  City. 

STAFF  COMMENT 


w 


FIG.    3 

A  useful  circuit  for  plate  detection 


AN  UNDER  VIEW  OF  THE  DEVICE 
DESCRIBED     BY    MR.      REPLOGLE 


detection.  The  sensitivity  of  the  detecting  circuit 
is,  however,  generally  lessened.  In  the  case  under 
consideration,  the  loss  in  signal  strength  is  prob- 
ably negligible  due  to  the  fact  that  the  relatively 
low  plate  potential  is  secured  by  increasing  the 
resistance  in  the  plate  circuit  of  the  detector 
tube  to  approximately  ten  times  the  value  em- 
ployed in  the  grid  current  detecting  system. 
Increasing  the  value  of  the  external  plate  resis- 
tor in  a  resistance-coupled  amplifier,  while  still 
maintaining  the  applied  plate  voltage  at  an 
optimum  value  for  detection,  increases  the  input 
to  the  amplifier,  which  in  this  instance,  partially 
compensates  the  loss  in  detecting  efficiency. 

Adjusting  Cone  Loud  Speakers 

FOR  THE  proper  adjustment  of  a  cone  loud 
speaker,  it  is  essential  that  the  pin  be 
exactly  centered  in  the  collar  at  the  apex.  It 
often  happens  that  in  the  rough  handling  of 
transportation  the  movement  of  the  loud 
speaker  is  shifted  slightly  from  dead  center  with 
the  result  that  there  is  a  strong  tension  on  the 
pin.  This  limits  the  amount  of  power  the  loud 


ITH  coils  de- 
signed for  tubes 
having  the  characteris- 
tics of  the  20 1 -A  type 
tube,  the  substitution 
of  alternating-current 
tubes  of  a  lower  input 
impedance  will  neces- 
sarily result  in  the  loss 
of  selectivity,  generally 
accompanied  with  an 
increase  in  sensitivity. 
These  effects  can  be 
compensated,  as  sug- 
gested by  Mr.  Bennett, 

by  increasing  the  grid  bias  applied  to  the  radio- 
frequency  tubes.  It  will  be  found  that,  at  the 
point  at  which  the  selectivity  is  equal  to  that  of 
the  d.  c.  set,  the  sensitivity  will  also  have  been 
readjusted  to  the  same  degree  characterizing  the 
original  battery  receiver. 


-AAAAA/V 

1000Q 

FIG.    4 

A  simple  arrangement  for  the  adjusting  of  cone 

loud    speakers.    Unless   properly   adjusted,    the 

cone  loud  speaker  will  not  give  its  maximum 

undistorted  volume 


r)RODUCTS  of  radio  manufacturers  whether 
±  new  or  old  are  always  interesting  to  our 
readers.  These  pages,  which  will  be  a  regular  feature 
of  RADIO  BROADCAST  from  this  issue  on  will  ex- 
plain and  illustrate  certain  products  which  have 
been  selected  for  publication  because  of  their  special 
interest  to  our  readers.  This  information  is  pre- 
pared by  the  Technical  Staff  and  is  in  a  form  which 
we  believe  will  be  most  useful.  We  have,  wherever 
possible,  suggested  special  uses  for  the  device  men- 
tioned. It  is  of  course  not  possible  to  include  all 
the  information  about  [each  device  which  is  avail- 
able. Each  description  bears  a  serial  number 
and  if  you  desire  additional  information  direct 
from  the  manufacturer  concerned,  please  address  a 
letter  to  the  Service  Department,  RADIO  BROAD- 
CAST, Garden  City,  New  York,  referring  to  the 
serial  numbers  of  the  devices  which  interest  you 
and  we  shall  see  that  your  request  is  promptly 
handled. — THE  EDITOR. 


A  Complete  A.  C.  Adapter  Unit 

X2I 

Device:  Marathon  A.  C.  Harness  equipment. 
Consists  of  a  cable  conductor,  a  transformer,  sup- 
plying the  correct  voltage  for  Marathon  tubes, 
type  AC  608,  and  a  volume  control.  The  Mara- 
thon a.  c.  tube  is  of  the  heater  type  and  is  rated 
at  6  volts  and  I  ampere.  Manufactured  by  the 
Northern  Manufacturing  Company.  Price:$}o.oo 
(5  or  6-tube  kit);  seven  and  eight-tube  units 
available. 

Application:  In  order  to  make  the  conversion  of 
a  d.  c.  set  to  a.  c.  operation  a  simple  matter  using 
Marathon  tubes,  this  company  is  supplying  the 
accessory  apparatus  (transformer,  cable,  and 
volume  control)  required.  It  should  be  under- 
stood that  this  apparatus  is  made  especially  for 
use  with  Marathon  tubes;  the  transformer  volt- 
age is  incorrect  for  other  types  of  a.  c.  tubes. 
The  Marathon  a.  c.  tube  is  equipped  with  two 


New  Apparatus 


Complete  A.  C.  Push-Pull  Amplifier 

X22 

Device:  Samson  Power  Audio  Amplifier,  Types 
PAM-i6  and  PAM-iy  for  use  with  radio  re- 
ceivers or  phonograph  pick-ups.  Both  types  are 
exactly  the  same  except  that  the  type  PAM-iy 
is  equipped  to  supply  40  milliamperes  at  120 
volts  to  the  field  winding  of  a  Magnavox,  or 
similar  dynamic  type  loud  speaker.  The  amplifier 
is  a  two-stage  transformer-coupled  unit  and 
consists  of  an  input  transformer  followed  by  a 


THE    MARATHON    A.    C.    KIT 


SAMSON    PHONOGRAPH    OR    RADIO 
AMPLIFIER 

type  227  a.  c.  tube  which  in  turn  feeds  into  the 
primary  of  a  push-pull  transformer.  Two  210 
type  tubes  are  used  in  the  push-pull  stage.  The 
filaments  of  the  210  type  tubes  are  operated  on 
a.  c.  and  plate  power  for  them  is  obtained  from 
a  rectifier-filter  system  using  a  type  281  tube.  As 
indicated  in  the  circuit  diagram 
one  of  the  input  leads  is  shielded. 
This  lead  connects  the  input  of 
the  amplifier  to  the  output  of 
the  detector  in  the  radio  re- 
ceiver (or  output  of  a  phono- 
graph pickup  if  one  is  used). 
Electrically  the  device  has  been 
arranged  to  conform  with  the 
underwriters'  specifications,  all 
the  wiring  being  entirely  en- 
closed. The  terminals  of  the 
audio  transformers  project 
down  through  the  base  of  the 
transformers  into  the  sub-base, 
and  are  therefore  unexposed. 


YAXLEY  S    POWER    CONTROL 

Manufactured  by  the  SAMSON  ELECTRIC  MAN- 
UFACTURING COMPANY.  Price:  $125.00. 
Application:  This  amplifier  can  be  connected  to 
the  output  of  the  detector  tube  in  a  radio  re- 
ceiver, being  used  therefore  instead  of  the  ampli- 
fier in  the  set,  or  it  may  be  used  in  conjunction 
with  a  phonograph  pick-up  to  reproduce  phono- 
graph records.  At  a  recent  R.  M.  A.  meeting, 
Mr.  Cotton  of  the  Samson  Company  demon- 
strated the  amplifier  to  two  of  the  staff  of  RADIO 
BROADCAST  Laboratory  and  the  reproduction 
from  phonograph  records  was  excellent.  There 
was  absolutely  no  hum  audible  in  the  Western 
Electric  540  AW  cone  used.  The  unit  is  beauti- 
fully finished  and  is  very  well  arranged  mechan- 
ically and  electrically.  Complete  data,  blue 
prints,  etc.,  are  available  from  the  Samson 
Company. 


HOW    TO    USE    THE    YAXLEY    POWER 
CONTROL 


extra  terminals  on  the  side  of  the 
tube  base  and  the  filament  trans- 
former terminals  need  merely  be 
connected  to  these  convenient  termi- 
nals using  the  harness  supplied  for 
the  purpose  in  this  kit,  and  the 
tubes  plugged  into  the  regular 
sockets  in  the  receiver.  No  adapters 
are  required.  This  is  a  distinct  ad- 
vantage when  space  is  limited 
for  these  tubes,  when  installed,  will 
project  no  higher  than  the  stor- 
age battery  type  tubes  used 
formerly  in  the  set.  When  226  and 
227  type  tubes  are  used  with  the 
necessary  adapters  the  overall 
.  height  of  the  tube  and  adapter 
is  greater  than  that  of  a  storage 
battery  tube  and  this  fact  will, 
in  some  a.  c.  conversion  jobs,  give 
some  difficulty  and  necessitate  re- 
arrangement of  some  apparatus. 


Shield  Symphonic 


CIRCUIT   OF    SAMSON    AMPLIFIER 
35 


At  Last  —  Automatic 
Power  Control 


Device:  Yaxley  Full  Automatic 
Power  Control.  For  the  automatic 
control  of  the  power  units  used  with 
a  radio  receiver.  Manufactured  by 
YAXLEY  MANUFACTURING  COMPANY. 
Price:  $7.50. 

Application:  This  device,  designed 
automatically  to  control  a  receiver 
installation  operated  from  a  B  supply 
and  a  trickle-charger  storage  battery 
combination,  functions  (a)  to  turn 
on  the  trickle  charger  and  turn  off 
the  B  power  unit  when  the  set  is 
turned  off,  (b)  turn  off  the  trickle 
charger  and  turn  on  the  B  power 
unit  when  the  set  is  turned  on  and, 
(c)  cut  out  the  trickle  charger  when 
the  battery  is  fully  charged.  All  of 


36 


RADIO  BROADCAST 


MAY,  1928 


this  is  accomplished  automatically  by  merely 
turning  the  filament  switch  on  the  receiver  off 
and  on.  It  is  evident  from  the  description  above 
that  the  functioning  of  this  device  differs  from 
that  of  an  ordinary  power  control  device  in  that 
a  relay  in  this  unit  is  adjusted  to  cut  out  the 
trickle  charger  when  the  battery  is  fully  charged 
so  that  there  is  no  possibility  of  overcharging  the 
battery.  The  device  will  function  with  sets  having 
any  number  of  tubes. 


TOBE  S    INTERFERENCE    FILTER 


Heavy-Duty  Interference  Filter 

X24 

Device:  Interference  Filter  No.  2.  Consists  of  a 
combination  of  filter  choke  coils  and  filter  con- 
densers, all  assembled  in  a  single  case.  Manu- 
factured by  the  TOBE  DEUTSCHMANN  COMPANY. 
Price:  $15.00. 

Application:  This  filter  is  designed  for  use  in  con- 
junction with  small  motors  and  other  devices 
which  are  acting  as  sources  of  radio  interference. 
This  filter  may  be  used  with  motors  rated  up  to 
5  horsepower;  for  smaller  motors,  interference 
filter  No.  I  may  be  used.  The  filter  is  connected, 
in  series  with  the  power  line,  close  to  the  piece  of 
apparatus  producing  the  interference.  The  Tobe 
Deutschmann  Company  will  supply  any  special 
filter  that  may  be  necessary  for  unusual  cases. 


GENERAL   RADIO    PUSH-PULL  AMPLIFIER 

A.  C.  or  D.  C.  Push-Putt  Amplifier 
Complete 

X25 

Device:  Push-pull  Power  Amplifier  Type  441. 
The  filament  wiring  is  arranged  so  that  the 
filaments  may  be  lighted  from  either  a.  c.  or  d.  c. 
The  input  impedance  of  this  amplifier  is  30  hen- 
ries and  the  turns  ratio  of  the  input  transformer 
to  the  entire  secondary  is  4.5.  The  output  trans- 
former has  a  step-down  ratio  in  voltage  of  3.5 
to  I,  to  adapt  the  tube  to  the  loud  speaker  im- 
pedance. This  gives  a  good  ratio  for  1 12  and 
226  type  tubes.  If  171  type  tubes  are  used  it  will 
be  better  to  connect  the  loud  speaker  between 
one  plate  terminal  and  the  B  Plus  terminal  of 


the  output  transformer.  Completely  assembled. 
Manufactured  by  the  GENERAL  RADIO  COM- 
PANY. Price:  $20.00. 

Application:  For  use  as  a  last  stage  amplifier  in 
conjunction  with  any  standard  receiver.  Any 
type  of  tube  may  be  used  in  the  amplifier,  the 
choice  depending  on  the  amount  of  voltage 
available  for  driving  the  unit  and  upon  the 
amount  of  power  output  that  is  desired.  This 
push-pull  amplifier  might  be  used  with  1 12  or  120 
type  tubes  where  moderate  amounts  of  power  are 
desired  and  with  171  type  tubes  when  greater 
power  is  required.  An  amplifier  of  this  type,  in 
use  in  RADIO  BROADCAST  Laboratory  for  some 
time,  has  been  giving  very  satisfactory  results. 

1/olume  Control  Unit 

\26 

Device:  Table  Type  Clarostat.  Consists  of  a 
Clarostat  variable  resistance,  mounted  in  a 
small  metal  case,  and  supplied  with  extension 
cords  so  that  it  may  easily  be  connected  between 
the  receiver  and  the  loud  speaker.  Manufactured 
by  the  AMERICAN  MECHANICAL  LABORATORIES. 
Price:  $2.50. 

Application:  A  convenient  accessory,  readily  at- 
tached to  any  radio  receiver,  to  control  the 
volume  of  signal  from  the  loud  speaker.  And  as 
the  advertisements  say,  it  will  control  the  volume 
from  a  "whisper  to  a  roar." 

Although  the  device  is  primarily  intended  for 
use  as  a  volume  control  in  the  loud  speaker  cir- 
cuit, there  is  no  reason  why  it  can't  be  put  to  any 
of  the  other  uses  for  which  a  Clarostat  is  suited, 
such  as  controlling  oscillations  in  the  r.  f.  ampli- 
fier, by  connecting  it  in  series  with  the  B+  lead 
to  the  radio  frequency  tubes.  This  device  might 
also  be  used  as  a  volume  control  when  con- 
nected in  parallel  across  the  antenna  and  ground 
of  a  receiving  set  installation. 

Filament  Transformer  for  A.  C. 
Tubes 

X27 

Device:  A.  C.  Filament  Lighting  Transformer 
Model  T-i.  Supplies  following  voltages: 

I i  volts — Capacity  for  seven  type  226  tubes 
25  volts — Capacity  for  four  type  227  tubes 
5  volts — Capacity  for  two  type  1 12  or  171  tubes 
The  transformer  is  arranged  with  a  flexible 
lead  to  be  plugged  into  one  of  three  possible 
jacks  which  permit  the  transformer  to  be 
operated  on  line  voltage  from  80  to  125  volts. 
Condensers  and  center-topped  resistors  neces- 
sary for  a.  c.  tubes  contained  in  transformer 
case.  Manufacturer:  HAROLD  J.  POWER,  INC. 
Price:  $10.00. 

Application:  May  be  used  to  supply  filament 
current  to  a.  c.  tubes  in  a  radio  receiver.  The 
flexible  lead  by  which  different  line  voltages  can 
be  compensated  is  an  excellent  feature  for  a.  c. 
tubes,  especially  the  227  heater  type,  which  have  a 
very  short  life  if  supplied  with  excessive  filament 
voltage.  Wiring  diagrams  of  various  standard 
receivers  revised  for  a.  c.  operation  may  be  ob- 
tained by  writing  the  manufacturers  of  this 
device. 

Drum  Dial  and  Adjustable  Gang 
Condenser 

X28 

Device:  Gang  Condenser  and  Drum  Dial.  The 
apparatus  contains  the  following  features: 

I.  All  of  the  condensers  are  mounted  on  a 
single  shaft  and  the  condensers  may  be  ad- 
justed to  any  desired  spacing  between  them 
by  merely  loosening  two  set  screws  and  slid- 


PRECISE     DIAL    AND    GANG    CONDENSER 


ing  the  condenser  along  the  shaft  to  the  de- 
sired position. 

2.  Each  condenser  is  equipped  with  an  ad- 
justment for  slightly  altering  its  capacity,  so 
that   accurate   tuning  of  each  circuit   in   a 
single-control  set  can  be  accomplished.  The 
photograph   illustrates  such  an  adjustment 
being  made,  a  procedure  which  is  only  neces- 
sary when  the  set  is  placed  in  operation  for 
the  first  time. 

3.  The    spacing    between    the    condenser 
plates  is  quite  large  so  that  the  capacity  of 
the  condenser  will  not  be  affected   to  any 
considerable  extent  by  variation  in  the  thick- 
ness of  the  plates. 

4.  Any  number  of  condensers  may  be  used 
in  the  assembly.  Each  condenser  has  a  capacity 
of  0.00035  mfd.  The  drum  dial  is  equipped  for 
a  dial  light  and  reads  from  o.  to  100,  the  scale 
being  also  approximately  calibrated  in  wave- 
lengths.    Manufactured     by     the     PRECISE 
MANUFACTURING   COMPANY.     Price:     (drum 
dial   assembly,   $5.00;    variable   condensers, 
0.00035     mfd.,    $6.00).      Application:    May 
be  used  in  constructing  a  single-control  re- 


Loud  Speaker 


X29 


Device:  Rola  Table  Type  Loud  Speaker,  Model 
20.  Finished  in  hand-rubbed  walnut,  nj  inches 
high,  i  if  inches  wide  and  6f  inches  deep.  Fre- 
quency range,  according  to  the  manufacturers, 
is  approximately  70  to  5000  cycles.  The  loud 
speaker  is  equipped  with  a  filter  to  suppress  the 
higher  frequencies.  The  armature  of  the  unit  is 
laminated,  evidently  to  obtain  higher  efficiency. 
Manufactured  by  the  ROLA  COMPANY.  Price: 
$35.00. 

Application:  This  loud  speaker  may,  of  course, 
be  used  with  any  standard  radio  receiver.  The 
manufacturers  recommend  the  speaker  espe- 
cially for  use  with  a.  c.  sets,  because  of  its  "tend- 
ency to  suppress  and  minimize  the  residual  hum 
characteristic  of  most  a.  c.  sets." 


NEW    ROLA    CONE 


C4  C2      R8       R3 


B+Amp.  |  B+135V     Bt45V 
IshA.F. 

225V. 


An  A.C*  Screen-Grid  Receiver 


ATERNATING-current       operation       of 
screen-grid  tubes  has  been  in  the  minds 
of  many  experimenters,  judging  from  the 
amount  of  correspondence  received  by   RADIO 
BROADCAST,  and  by  the  number  of  visitors  to  the 
Laboratory   who   have   broached    this   subject. 
The  receiver  described  here  is  the  first  that  has 
come  into  the  Laboratory  which  shows  how  this 
may  be  accomplished.  After  all  the  speculation 
regarding  the  possibilities  of  a.  c.  operation  of 
this  new  tube,  the  trick  of  how  to  do  it  seems  to 
be  no  trick  at  all;  all  one  needs  is  a  source  of 
a.  c.  voltage  of  the  proper  value — 3.3.  volts. 
The   receiver,   originally   designed   for   d.    c. 


operation,  was  described  in  the  March  RADIO 
BROADCAST.  It  covers,  with  plug-in  coils, 
all  frequencies  between  100  and  10,000  kc.,  and 
consists  simply  of  a  stage  of  radio-frequency 
amplification  using  the  screen  grid-tube,  a  re- 
generative detector,  and  two  stages  of  audio- 
frequency amplification,  transformer-coupled. 
All  tubes  in  the  present  adaptation  of  this  re- 
ceiver operate  from  a.  c.,  the  voltage  for  the 
screen-grid  tube  being  obtained  by  connecting  in 
series  the  1.5-  and  the  2.5-volt  windings  of  a 
standard  filament  transformer,  and  then  drop- 
ping the  resultant  4  volts  to  the  proper  value, 
3.3,  by  means  of  a  4-ohm  resistance.  The  output 


tube  is  a  II2-A  and  the  detector  and  first  audio 
amplifier  are  heater  type  c-32y  or  uv-22y  tubes. 
In  the  proper  places  in  the  circuit  are  bias  re- 
sistances so  that  not  even  C  batteries  are  neces- 
sary for  the  receiver's  operation. 

In  the  Laboratory  the  use  of  a.  c.  on  the  screen- 
grid  tube's  filament  contributed  no  a.  c.  hum  to 
the  output  from  the  loud  speaker.  When  listening 
with  a  pair  of  phones  across  the  output,  the  hum 
which  is  audible  is  no  greater  than  that  of  any 
two-stage  audio  amplifier  and  detector  operating 
entirely  from  a.  c. 

The  difference  in  circuit  between  the  original 
d.  c.  receiver  and  the  present  one  can  be  deter- 
mined by  reference  to  the  accompanying  dia- 
grams, Figs.  I  and  2.  Aside  from  the  a.  c.  wiring, 
and  the  addition  of  C  bias  resistors  in  their 
proper  places,  another  change  is  that  the  grid 
leak  is  placed  across  the  grid  condenser  instead 
of  from  grid  to  plus  filament.  This  is  because  the 
heater  type  of  tube  has  no  filament  proper,  and 
all  grid  and  plate  returns  are  connected  to  the 
fifth  or  cathode  post  of  the  tube. 

Reference  to  the  diagram  of  the  a.  c.  model, 
Fig.  2,  shows  the  following  resistances  which  are 
not  in  the  d.  c.  set:  Ri,  1500  ohms,  to  furnish  C 
bias  for  the  screen-grid  tube;  R2,  64  ohms,  center- 
tapped,  across  the  filament  of  this  tube,  the 
center  point  connecting  to  ground  through  the 
bias  resistance;  RI;  Rs,  4  ohms,  to  drop  the  output 
voltage  of  the  transformer  to  3.3  volts  for  the 
filament  of  the  screen-grid  tube;  R<,  1500  ohms, 
in  the  grid  return  lead  of  the  first  audio  tube  to 
supply  C  bias  to  this  tube;  RS,  2000  ohms,  to 
furnish  C  bias  to  the  last  tube;  and  R6,  another 
64-0(101  center-tapped  resistance  for  the  last 
tube,  the  center  connecting  through  the  bias 
resistance  to  ground.  There  are  also  two  o.  i-mfd. 
condensers  across  the  center-tapped  and  bias 
resistances  on  the  screen-grid  tube  to  act  as  radio- 
frequency  bypasses,  and  there  is  a  5OO,ooo-ohm 
potentiometer  across  the  secondary  of  the  first 
audio  transformer  to  act  as  a  volume  control.  A 
i-mfd.  condenser  across  the  C  bias  resistor  of  the 
final  tube  is  optional.  Its  inclusion  will  provide 
better  bass  note  reproduction.  Naturally.  UY 
sockets  must  be  used  in  place  of  standard  sockets, 
for  the  two  heater  type  tubes  now  used  in  the 
detector  and  first  audio  stages.  Otherwise  the 
present  receiver  is  exactly  like  the  one  described 
in  March.  It  covers  the  same  frequency  ranges, 


=  Ground 


Dial  Lights 


FIG.     I 
A  schematic  diagram  of  the  four-tube  receiver  as  originally  designed  for  d.c.  operation 

37 


38 


RADIO  BROADCAST 


MAY,  1928 


uses  the  same  parts,  is  laid  out 
on  the  pane!  and  baseboard 
similarly,  and  its  operation 
differs  not  at  all. 

As  stated  before,  to  get  3.3 
volts  for  the  first  tube's  fila- 
ment it  is  necessary  to  con- 
nect in  series  the  2.5-volt  and 
the  i.5-volt  windings  of  the 
standard  filament  trans- 
former. If  these  windings  are 
not  connected  together  prop- 
erly, the  screen-grid  tube  will 
not  light.  No  harm  can  be 
done,  however,  by  such  a  con- 
nection, and,  therefore,  the 
builder  can  easily  determine 
which  connection  is  proper. 

The  voltage  on  the  fila- 
ment of  the  screen-grid  tube 
is  not  critical  as  to  hum;  the 
variation  in  voltages  occurring 
in  practice,  due  to  line  fluctuations  etc.,  are  not 
great  enough  to  cause  hum. 

While  the  arrangement  used  .or  t.ie  operation 
of  the  222  tube  in  the  four-tube  set  has  not  been 
tried  with  two  or  three  r.  f.  stages  yet,  there  ap- 
pears no  reason  why  it  should  not  function  satis- 
factorily, and  the  application  of  a.  c.  operation 
to  two-  and  three-stage  screen-grid  r.  f.  amplifiers 
should  prove  a  most  fertile  field  of  experiment. 
The  parts  used  for  constructing  the  four-tube 
a.  c.  screen-grid  receiver  are  listed  below.  While 
the  parts  specified  are  recommended,  the  experi- 
menter may  substitute  other  makes  of  parts 
electrically  equivalent  with  safety: 

LI — S-M  1 1 1 A  Antenna  Coil $  2.50 

Lj— S-M  1 1486  R.  F.  Coil 2.50 

Two  S-M   515   Universal    Interchange- 
able Coil  Sockets 2.00 

Li— Two  S-M  275  R.  F.  Chokes i  .80 

T — Two  S-M  240  Audio  Transformers         12.00 
Ci — Two  S-M  320  0.0003 5-Mfd.    Vari- 
able Condensers 6.50 

Q — S-M    342    0.00007 5-Mfd.    Midget 

Condenser    1 .50 

Ca — Sangamo  o.oooi  5-Mfd.  Condenser 

with  Leak  Clips .50 

Ct — Two  Fast  i-Mfd.  Condensers  ....         1.80 
C6 — Two    Sprague     o.i-Mfd.     Bypass 

Condensers i  .70 

Ri,  R4 — Yaxley  ijoo-Ohm  Grid  Resis- 
tors            i  .00 

R2,    Re— Two    Frost    FT64    Balancing 

Resistors 1 .00 

R3 — Carter  4-Ohm  Resistor .25 


THE  CONTROLS  ARE  GROUPED  CLOSELY  TOGETHER  ON  THE  FRONT  PANEL 


R6 — Yaxley  20oo-Ohm  Grid  Resistor.  .  .  .50 
RT — Durham  5-Megohm  Grid  Leak.  ...  .25 
Rs — Carter  5OO,ooo-Ohm  Volume  Con- 
trol Potentiometer 2.00 

Thirteen  Fahnestock  Connection  Clips  .65 

Two  S-M  511  Tube  Sockets 1 .00 

Two  S-M  512  Tube  Sockets 1.50 

Two  S-M  805  Vernier  Drum  Dials.  .  .  .  6.00 
7x17x3"  Wood   Baseboard,  with  Hard- 
ware   1.50 

i   Van   Doom  7x18"  Decorated  Metal 

Panel 3.00 

AND   THE    FOLLOWING    ACCESSORIES 

ux-112-A  (cx-312-A)  Power  Tube 

ux-222  (cx-322)  Screened  Grid  Tube 

Two  uv-227  (c-j27)  Heater  Tubes 

Cone  Loud  Speaker 

Filament-Lighting    Transformer  with    ij-,   2j- 

and  5-Volt  Secondaries,  such  as  the  S-M  247 

Illustrated. 
Three    45-Volt    Heavy-Duty    B    Batteries,    or 

Any  Standard  Socket  Power  Unit  Capable  of 

Accurate  Voltage  Adjustment. 

The  coils  listed  above  are  suitable  to  cover  the 
broadcasting  frequencies.  Other  coils  from  the 
same  manufacturer  make  the  receiver  truly 
universal  insofar  as  wavelength  range  is  con- 
cerned. 

To  hook  this  set  up,  it  is  simply  necessary  to 
connect  the  B  batteries  (or  the  socket  power 
supply),  loud  speaker,  antenna  and  ground,  to 
the  clips  marked  in  the  illustration,  and  to  insert 
the  tubes.  The  filament  transformer  must  be 


f  0.000075  cnfd. 


CX-312-A 


connected  to  its  appropriate  clips  by  means  of 
carefully  twisted  wires.  Preferably,  it  should  be 
situated  a  foot  or  so  from  the  audio  transformers 
in  the  receiver. 

The  receiver  operates  exactly  as  any  other  set 
of  its  type,  the  two  station  selector  dials  serving 
to  tune-in  the  different  stations  in  the  broad- 
cast band  of  200  to  550  meters,  the  midget  re- 
generation condenser  controlling  sensitivity 
(regenerative  amplification)  and  the  volume 
knob  controlling  loud  speaker  volume.  No 
"On-Off"  switch  has  been  provided  in  the  set 
for  it  is  assumed  that  the  socket-power  unit  or 
filament  transformer  used  will  be  provided  with 
a  switch  either  in  the  instrument  itself,  or  in  the 
connecting  cord,  or  if  in  neither,  the  set  may 
easily  be  turned  on  or  off  at  the  lamp  socket  to 
which  the  power  unit  supply  cord  is  attached. 
Using  the  standard  1 1  i-A  and  i  I4-SG  coils  the 
set  tunes  from  200  to  550  meters,  while  by 
dropping  the  r.  f.  stage  and  connecting  the 
antenna  to  point  3  of  the  detector  coil  socket 
through  a  small  o.oooo25-mfd.  midget  condenser 
the  set  will  cover  the  shorter  wavelength  ranges 
from  30  to  75  meters  with  1 14-C  coil,  or  70  to 
210  meters  with  a  114-6  coil.  Waves  above  550 
meters  may  be  received  with  a  1 1  i-D  and  1 14-0 
coils  (500  to  1500  meters)  or  a  1 1  i-E  and  i  I4-E 
coil  (1400  to  3000  meters).  Although  there 
are  no  American  broadcasting  stations  operating 
above  550  meters  there  is  great  sport  for  those 
who  know  the  code  on  these  lower  frequency 
bands.  Ships  at  sea, 
compass  stations,  air- 
mail stations,  time  sig- 
nals, and  navy  vessels 
— all  have  wavelengths 
covered  by  this  receiver. 
It  will  be  necessary  to 
shunt  the  regeneration 
condenser  with  a  fixed 
capacity  of  o.oooi-mfd. 
to  get  good  oscillation 
control  when  the  D  and 
E  range  coils  are  used. 


1  VoltS 


5V.          B»A.F. 
A.C. 


FIG.  2 
Circuit  diagram  of  the  a.c.  screen  grid  receiver 


£ 

0.00015,mfd. 

'  3 

"Time  Amplifier 


Q        O        O        Q 

fr326          CX- 326  CX- 326  C-327 


FIG.    I 

Switching  provides  for  the  use  of  this  circuit  either  as  a  super-heterodyne  or  as  a  single-circuit  receiver 


By  Dana  Adams 


€ 


WE  receiver  described  in  this  article  has 
several  unique  points  of  interest  which 
distinguish  it  from  the  commonplace.  In 
the  first  case,  it  is  a.c.  operated,  a  feature  which 
is  becoming  more  and  more  popular.  The  most 
interesting  feature  of  the  receiver,  however,  is 
the  fact  that,  by  the  mere  flip  of  a  switch,  the 
degree  of  selectivity  and  sensitivity  of  the  sys- 
tem may  be  augmented  or  decreased,  depending 
upon  the  requirements  of  the  operator  and  his 
geographical  location  with  respect  to  the  station 
he  wishes  to  hear.  The  circuit,  in  its  most  sensi- 
tive form,  is  a  super-heterodyne  employing  a 
three-stage  intermediate-frequency  amplifier. 
The  switching,  which  controls  the  selectivity  and 
sensitivity,  provides  for  three  circuit  arrange- 
ments as  follows: 

ist  Position:  The  receiver  is  converted  into  a 
single-circuit  receiver  with  one  tuning  control 
and  one  volume  control,  the  output  of  the  de- 
tector tube  inputting  directly  to  the  audio 
amplifier. 

2nd  Position:  Same  as  ist  Position  with  the 
exception  that  a  series  condenser  in  the  antenna 
circuit  is  switched  in  by  means  of  a  Yaxley  No. 
10  antenna  switch,  thus  adding  a  further  tuning 
control,  but  at  the  same  time  improving  sensi- 
tivity. 

3rd  Position:  The  complete  super-heterodyne 
receiver  is  thrown  into  operation,  a  third  main 
tuning  control  being  added.  The  antenna  tuning 
condenser  need  not  necessarily  be  switched  into 
circuit  in  this  case. 

The  switch  used  for  switching  from  single-circuit 
receiver  to  super-heterodyne  receiver  is  a  Yaxley 
No.  6}  triple-pole  switch.  In  Fig.  I  (the  complete 
circuit  diagram  up  to  the  output  of  a  single- 
stage  audio  amplifier),  various  connections  to 
this  switch  are  indicated  by  number  but  are  not 
grouped.  The  numbers  for  the  switch  terminals 
are  determined  by  counting  from  right  to  left 
from  a  rear  view  of  the  switch. 

Fig.  I  shows  a  coil  and  the  condenser  in  series 
with  the  antenna.  Variation  of  this  condenser 
tunes  the  antenna  to  any  desired  frequency 
in  the  same  manner  that  the  grid  circuit  of  a  tube 
is  tuned,  with  a  consequent  increase  in  signal 
strength.  At  the  same  time,  the  strength  of  sig- 


nals flowing  in  the  antenna  circuit  at  other  than 
the  resonant  frequency  is  reduced,  following 
the  law  of  all  series-tuned  circuits.  Laboratory 
measurements  show  this  gain  at  the  resonant 
frequency  to  be  equal  to  that  of  one  radio- 
frequency  stage.  Coupling  to  the  detector  cir- 
cuit is  obtained  through  a  small  variable  coil, 
Li,  which  is  a  part  of  the  Samson  No.  3 1  coupler 
(which  comprises  Lj,  La,  and  L^).  This  coupling 
coil,  particularly  when  the  antenna  tuning  is 
used,  is  generally  set  very  near  the  minimum 
coupling  point,  with  a  consequent  increase  in 
selectivity. 

Having  made  the  antenna  circuit  and  the 
coupling  method  as  efficient  as  possible  we  turn 
next  to  the  first  detector.  This  tube  is  regenera- 
tive with  the  sensitive  grid  leak  and  condenser 
method  of  detection  and  at  this  point  the  circuit 
departs  from  the  ordinary.  The  Yaxley  No.  63 
triple-pole  switch  is  used  here  to  cut  out  the  os- 
cillator and  intermediate  stages  of  the  receiver, 
at  the  same  time  transferring  the  first  detector 
plate  lead  from  the  intermediate  amplifier  in- 
put to  that  of  the  audio  amplifier.  The  result  is 
a  highly  efficient  regenerative  receiver  with  an 


audio  amplifier.  The  middle  dial  may  be  used 
alone  in  tuning-in  the  local  programs  with  the 
antenna  coupling  acting  as  a  volume  control. 
If  additional  efficiency  is  required,  a  flip  of  the 
antenna  switch  makes  the  antenna  tuning  feature 
immediately  available. 

A  change  of  position  of  the  three-pole  switch 
returns  the  detector  plate  to  its  normal  connec- 
tion in  the  super-heterodyne  circuit,  at  the  same 
time  lighting  the  oscillator  and  intermediate- 
amplifier  tubes,  which  gives  us  a  two-  or  three- 
dial  super-heterodyne  receiver.  Instead  of  the 
ordinary  coupling  coil  method  of  introducing 
the  heterodyne  frequency  to  the  detector  grid 
circuit  this  is  done  by  placing  the  oscillator  coil 
itself  in  inductive  relation  to  the  detector  coil. 
This  eliminates  the  losses  of  signal  strength 
frequently  caused  by  a  tightly  coupled  coil 
which  is,  in  most  cases,  at  ground  potential. 
The  oscillator  circuit  is  thus  made  entirely  in- 
dependent of  the  receiver  except  for  its  power 
supply.  The  oscillator  circuit  is  the  familiar 
modified  Hartley  circuit,  grounded  rotor  plates 
preventing  any  hand-capacity  while  tuning. 

The  beat  note  set  up  by  the  oscillator  and  first 


A    FRONT    VIEW    OF    THE    COMPLETE    RECEIVER 
39 


40 


RADIO  BROADCAST 


MAY,  1928 


detector  is  impressed  on  the  first  intermediate' 
frequency  amplifier  tube  grid.  The  reader  will 
no  doubt  recognize  the  intermediate  amplifier 
as  the  well-known  Silver-Marshall  "Jeweller's 
Time-Signal  Amplifier"  unit.  The  high  ampli- 
fication, the  sharp  cut  off  of  its  accurately  tuned 
air-core  transformers,  and  the  consistently  ex- 
cellent results  obtained  with  a  considerable 
number  of  these  units,  are  the  reasons  for  its 
selection  for  this  receiver. 

After  the  second  detector,  the  audio  compo- 
nent of  the  signal  is  amplified  by  one  stage  of 
audio  amplification.  A  choke  coil  together  with 
the  bypass  condenser  included  in  the  amplifier, 
combine  in  bypassing  the  radio-frequency  com- 
ponent of  the  signal  to  ground,  thereby  keeping 
it  out  of  the  audio  amplifier.  The  output  of  this 
stage  is  fed  to  the  second  audio  stage,  which  has 
been  omitted  in  the  circuit  diagram. 

To  combine  the  various  ideas  described  above 
in  a  receiver  employing  battery-operated  tubes 
is  an  easy  matter.  Fig.  2  shows  such  an  arrange- 
ment. True  electric  operation,  however,  is  con- 
venient and  obtained  in  simplest,  cheapest,  and 
least  troublesome  form  with  the  tubes  lighted 
from  an  alternating-current  source  of  supply. 
Tube  life  when  a.c.  tubes  are  used  is  an  impor- 
tant consideration.  The  writer's  experience  in- 
dicates that  excessive  filament  voltage  is  the 
cause  of  complaints  of  short  life  of  the  a.  c. 
tubes.  An  almost  total  lack  of  measuring  instru- 
ments is  responsible  for  this  condition  which 
time  and  an  increase  in  knowledge  will  undoubt- 
edly correct.  As  all  tubes  in  this  receiver  are 
worked  at  a  point  well  under  the  rated  voltage, 
uniform  and  highly  satisfactory  results  are  to 
be  expected,  the  voltage  adjustments  being  ex- 
tremely easy  to  make. 

GENERAL   CONSIDERATIONS 

HTHE  omission  of  a  number  of  details  from  the 
^  review  of  the  receiver,  while  enabling  the 
reader  to  obtain  a  clearer  idea  of  the  main  fea- 
tures, has  no  doubt  set  up  a  number  of  ques- 
tions. The  numbers  for  the  switch  terminals 
are  deterrnined  by  counting  from  right  to  left 
from  a  rear  view,  as  explained  previously.  The 
first  detector  and  oscillator  circuits  may  be 
easily  traced  with  this  information  at  hand. 
These  tubes  in  these  two  circuits  are  of  the  ca- 
thode type  in  order  that  the  beat  note,  tre- 
mendously amplified  in  the  intermediate  stages, 
will  be. absolutely  free  from  hum.  The  CX-J26 
(ux-226)  type  tube  is  used  in  the  three  inter- 
mediate stages,  the  2o-ohm  potentiometer,  Ra, 
across  the  filament  circuit,  providing  a  mid-tap 


No,  8 


NO.  3 


for  the  grid  returns.  The  looo-ohm  potentiom- 
eter, R2,  biases  the  grids  of  these  tubes  to  pre- 
vent oscillation  and  hum,  the  usual  method  of 
running  the  grids  positive  being  impossible 
where  alternating  current  is  employed.  The 
method  of  securing  the  bias  voltage  will  be  recog- 
nized as  that  used  in  biasing  the  last  audio 
stage  in  the  modern  power  amplifier.  A  50,000- 
ohm  variable  resistor,  R4,  is  shunted  across  the 
primary  of  the  audio  transformer  in  order  to 
provide  an  additional  means  of  reducing  the  vol- 
ume when  the  super-heterodyne  is  employed. 
The  remaining  resistor,  the  3Ooo-ohm  poten- 
tiometer, Ri,  provides  a  common  bias  voltage 
for  the  second  detector  and  first  audio  stages. 

The  adapter  which  is  necessary  in  order  that 
the  cathode  type  tube  may  be  employed  in  the 
standard  socket  in  the  "Time-Signal  Amplifier" 
is  omitted  from  the  diagram  for  the  sake  of  sim- 
plicity. It  is  referred  to  in  the  list  of  parts.  A 
detailed  account  of  this  device  will  be  found  later, 
in  the  wiring  instructions.  The  various  colored 
leads,  ten  in  number,  noted  in  the  diagram,  are 
provided  in  a  single  Jones  ten-wire  cable.  This 
enables  the  user  to  disconnect  the  power  from 
the  receiver  in  a  second  or  so.  A  Silver-Marshall 
filament  transformer  is  used  to  supply  the  two 
filament  voltages  for  the  a.c.  tubes  and  the  volt- 
age for  the  dial  lights.  Three  of  the  cable  wires 
provide  B  voltage  to  the  receiver  while  a  fourth 
connects  the  plate  of  the  first  audio  tube  to  the 
primary  of  the  second  transformer. 


\A7  ITH  a  grasp  of  the  main  facts  and  an  idea 
*  *  of  the  principles  employed,  the  construc- 
tion of  this  receiver  becomes  an  extremely  simple 
matter.  The  first  step  is  that  of  assembly.  All 
of  the  apparatus,  with  the  exception  of  the 
"Time  Amplifier,"  is  put  in  the  positions  noted 
in  Fig.  3.  The  pointers  listed  below  have  been 
gathered  from  the  experiences  of  a  number  of 
builders,  and  if  followed  carefully,  will  insure 
perfect  results. 

After  mounting  the  panels  and  dials  the  first 
point  to  be  noted  in  the  assembly  is  the  method 
of  mounting  the  condensers.  The  slotted  bars 
provided  with  the  dials  are  removed  and  a  one- 
inch  machine  screw  is  slipped  into  the  slot  in  the 
dial  frame.  The  three  collars  or  bushings  fur- 
nished with  each  dial  are  slipped  over  the  screws. 
The  condensers  are  then  held  in  the  position 
shown  in  the  photograph  and  the  screws  are 
threaded  into  the  holes  provided  in  the  conden- 
ser frames.  An  extremely  solid  mounting  is  the 
result.  The  tube  sockets,  audio  transformer, 


"Time Amplifier" 
0.002  mfd 

o     o     c56 


Dial  Lights 


90V.  6V.A-C.orDC.    B-      Gnd.       A-      45V    -4>5  C 


FIG.    2 
Circuit  arrangement  for  battery  operation 


switches,  bypass  condenser,  choke-coil,  the 
jo.ooo-ohm  resistor  on  the  panel,  and  the  an- 
tenna coil  require  no  special  description.  The 
remaining  resistors  are  mounted  on  the  resis- 
tor strip  which  is  raised  two  inches  above  the 
baseboard  by  brackets,  in  the  following  order: 
In  No.  I  position  place  the  jooo-ohm  poten- 
tiometer; No.  2,  the  looo-ohm  potentiometer; 
No.  3,  the  2o-ohm  potentiometer;  No.  4,  the 
5O,ooo-ohm  resistor. 

The  double  rotor  coupler  (consisting  of  L2, 
La,  U)  used  in  the  first  detector  circuit  to  secure 
variable  antenna  coupling  and  regeneration 
requires  altering  before  mounting.  All  but 
eight  turns  are  removed  from  the  antenna  coup- 
ling rotor,  L>,  which  is  controlled  by  the  lower 
of  the  two  knobs.  The  oscillator  coil  also  re- 
quires alteration  before  mounting.  Eight  turns 
are  removed  from  the  outside  end  of  the  large 
or  grid  winding  of  the  coil,  Ls.  This  is  done  so 
that  the  detector  and  oscillator  control  settings 
will  match  although  tuned  112  kc.  apart.  The 
wire  removed  from  this  coil  should  be  added  to 
the  plate  coil,  L«,  at  the  bottom,  insuring  suffi- 
cient feedback  to  cause  oscillation.  This  coil  is 
then  mounted  three  eighths  of  an  inch  from  the 
coupler,  as  shown  in  the  photograph,  to  insure 
proper  coupling. 

The  wiring  of  the  first  detector,  audio  stage, 
and  oscillator  circuits  is  the  next  step.  A  twisted 
pair  from  the  pink  and  blue  terminals  of  the 
cable  to  each  pair  of  dial  light  terminals  eli- 
minates these  from  further  calculation.  From 
the  yellow  and  black  terminals  another  twisted 
pair  is  connected  to  the  contacts  of  the  mid-tap 
resistor  mounted  on  the  filament  posts  of  the 
audio  tube  socket.  From  this  point  the  pair  is 
continued  to  the  detector  socket  and  from  there 
one  wire  goes  to  the  oscillator  tube  socket 
while  the  other  connects  to  Contact  No.  5  on 
the  triple-pole  switch.  A  wire  from  No.  4  con- 
tact on  the  switch  to  the  remaining  filament 
post  completes  the  wiring  of  the  heater  circuits. 
The  remaining  wiring  to  these  three  tubes  may 
be  easily  traced  from  the  diagram. 

All  filament,  cathode,  and  B  battery  wiring 
should  be  formed  along  the  main  cable,  as  shown 
in  the  photograph,  wherever  possible.  The  leads 
from  the  plate  of  the  detector  to  the  switch,  from 
the  antenna  coil  to  the  coupling  coil,  and  other 
leads  at  a  high  potential  from  a  radio-frequency 
standpoint,  should  be  formed  in  a  secondary 
cable  close  to  the  panel.  Avoid  right-angle 
bends  on  grid  and  plate  connections;  the  shorter 
they  are,  the  better.  In  wiring  the  oscillator  cir- 
cuit be  sure  that  the  grid  and  plate  connect  to 
the  outside  ends  of  their  respective  coils,  or  the 
tube  will  not  oscillate.  Pin-jacks  may  be  moun- 
ted at  the  ends  of  the  resistor  strip  so  that  a 
phonograph  pick-up  or  one  of  the  "home- 
broadcasting"  microphones  may  be  employed. 
One  pin-jack  should  be  connected  to  B  minus 
and  the  other  to  the  plate  terminal  of  the  audio 
transformer. 

The  drilling  instructions  for  the  resistor  strip 
are  shown  in  Fig.  3.  Only  two  of  the  three  con- 
nections on  the  looo-  and  3Ooo-ohm  potentiom- 
eters are  employed  as  their  function  is  that  of  a 
variable  resistor  rather  than  a  bridge  resistance 
in  this  circuit. 

The  "Time-Signal  Amplifier"  should  be  put 
in  position  next.  The  filament  wiring  should  be 
twisted  together  and  the  remaining  leads  run- 
ning the  length  of  the  receiver  should  be  formed 
into  the  main  cable.  The  B  minus,  plus  45  volt, 
and  plus  go  volt  connections  should  be  picked 
up  at  the  nearest  point  in  the  wiring  of  the 
other  tubes  and  connected  to  the  proper  posts 
on  the  amplifier. 

The  adapter  for  the  second  detector  tube, 
referred  to  previously,  is  provided  with  a  pair 


MAY,  1928 


A  FLEXIBLE  A.C.  SUPER-HETERODYNE 


41 


Cable  Block-,  Resistor  Strip 


Time  Amplifier 

o      o      o 


Osc. 
Cond. 


Sec. 
Cond. 

LAYOUT  OF  PARTS 


50,000  W 


Ant 
Cond. 


o                                           o                                              o 

Q                          0                            0 

£ 

>            -^-«            -£ 

>                     ^ 

~CM 

Y 

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<--   3"— 

„ 

*  415-"-,. 

•*-  -  --  4^5  *" 

<--  3-    -> 

FRONT  PANEL  LAYOUT 


< 

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*' 

Jc 

-I*"- 

•M^* 

RESISTOR  STRIP 
FIG.    3 

of  filament  leads,  the  pins  that  normally  would 
supply  filament  power  being  dummies.  These 
leads  are  twisted  together  and  connected  to  the 
filament  terminals  of  the  oscillator  tube  socket, 
the  detector  then  turning  on  or  off  with  the  rest 
of  the  intermediate  tubes.  The  grid  and  plate 
make  the  normal  connections  to  the  circuit 
through  the  adapter  pins  while  the  cathode  is 
brought  to  the  pin  normally  used  for  negative 
filament.  The  wire  connecting  to  the  correspond- 
ing post  on  the  socket  inside  the  can  should  be 
unsoldered  and  a  new  wire  run  out  of  the  shield 
from  this  post  and  connected  to  the  cathode  post 
of  the  audio  amplifier  tube  socket.  The  removal 
of  this  connection,  which  is  merely  a  connection 
to  the  shield,  does  not  disturb  the  circuit  in  any 
way.  The  bypass  shown  across  the  B  and  P 
terminals  of  the  amplifier  is  most  important,  as 
well  as  the  radio-frequency  choke  in  the  output 
lead  of  this  amplifier. 

The  receiver  is  now  ready  for  test.  To  do  this 
properly  the  power  unit  that  is  to  be  used  must 
be  at  hand.  A  few  suggestions  anent  this  unit 
will  undoubtedly  assist  those  who  are  not  fa- 
miliar with  this  adjunct  to  quality  reception. 
The  combination  of  a  full-wave  rectifier,  a  good 
filter  circuit,  and  a  voltage  regulator  tube  pro- 
vide the  best  possible  B  voltage  supply.  As  the 
unit  is  also  used  to  secure  C  bias,  its  freedom 
from  ripple  is  important.  Naturally  a  push-pull 
cx-3io  (ux-2io)  stage  represents  the  last  word 
for  a  tremendous  amount  of  undistorted  output 
although  a  cx-37i  a  (ux-iyi)  stage  will  be  found 
sufficient  in  the  average  home. 

The  first  step  in  testing  is  to  throw  the 
switch  to  the  single-circuit  receiver  position.  A 
minute  should  elapse  before  the  receiver  starts 
functioning.  The  jooo-ohm  resistor  should  be 
set  at  the  halfway  position.  Failure  to  operate 
may  be  readily  traced  in  this  simple  two-tube 
set.  Hum  audible  over  a  foot  from  the  loud 
speaker  indicates  either  oscillation,  in  which 
case  the  tickler  should  be  adjusted,  or  an  open 
circuit.  A  check  of  the  B  voltage  at  the  plate 
and  a  test  for  open  grid  circuits  is  sure  to  locate 
the  trouble.  The  panel  resistor  should  be  turned 


to  the  left  to  obtain 
greatest  volume.  After 
tuning  up  and  down  the 
dial  a  few  times  the  an- 
tenna tuning  should  be 
tested  by  opening  the 
switch.  Its  effect  will  be 
noticed  more  readily  on 
the  weaker  stations.  The 
dial  setting  may  be 
matched  within  a  few 
divisions  of  the  detector 
dial  by  putting  a  few 
turns  of  wire  in  series 
with  the  antenna.  This 
will  be  necessary  only 
where  a  short  antenna  is 
employed.  Up  to  150  feet 
may  be  used  without 
fear  of  broad  tuning,  as- 
suring a  stronger  signal 
from  distant  stations. 

TheosciHater  is  tested 
by  tuning-in  a  station 
in  the  middle  or  lower 
portion  of  the  wave  band 
and  temporarily  short- 
circuiting  contacts  Nos. 
4  and  5  of  the  switch. 
After  the  tube  has 
warmed  up  the  dial 
should  be  rotated.  A 
loud  heterodyne  squeal 
on  the  incoming  signal 
indicates  the  proper 

functioning  of  the  oscillator.  A  check  up  on 
the  connection  and  the  continuity  of  the  grid 
and  plate  circuits  will  readily  correct  any  trouble. 
The  third  step  in  the  testing  is  that  of  the 
intermediate  amplifier.  The  looo-ohm  resistor 
should  be  set  at  a  quarter  turn  from  the  zero 
bias  point,  the  1 5-ohm  potentiometer  at  the  mid- 
point, and  the  B  resistor  slightly  below  the  full- 
voltage  position.  A  turn  of  the  switch  and  a  few 
moments  wait  should  see  the  super-heterodyne 
in  operation.  A  rapid  succession  of  "birdies" 
when  the  oscillator  is  tuned  indicates  oscillation 
in  the  intermediate  stages.  This  is  the  only 
trouble  that  will  be  encountered  rf  the  wiring 
has  been  done  in  the  correct  manner.  It  is 
readily  corrected  by  reducing  the  filament  volt- 
age. An  o.  5-ohm  rheostat,  which  should  be  located 
at  the  filament  transformer  end  of  the  cable, 
is  the  remedy.  A  slight  readjustment  of  the 
bias  and  B-voltage  resistor  will  also  be  of  assis- 
tance. It  should  be  borne  in  mind  that  the  ampli- 
fier should  be  adjusted 
so  that  maximum  am- 
plification is  obtained 
at  all  times.  The  input 
is  controlled  by  the  an- 
tenna coupling  while 
the  resistor  across  the 
transformer  primary 
may  be  used  as  an 
auxiliary  means  of  re- 
ducing the  tremendous 
volume  that  may  be 
obtained,  to  a  reason- 
able level.  While  the 
rheostat  takes  care  of 
the  voltage  applied  to 
the  cx-326  (ux-226) 
tubes  in  excellent  fash- 
ion, care  should  be 
taken  that  the  cathode 
tubes  are  not  run  at 
an  excessive  voltage. 
If  the  receiver  is  to 
be  operated  from  an  A 
battery  and  is  toderive 


its  plate  voltage  from  either  batteries  or  power- 
supply  unit,  various  changes  must  be  made.  Three 
S-M  No.  51 1  sockets  will  be  required  in  place  of  the 
three  No.  512  ones  indicated  in  the  list  of  parts. 
Two  Carter  I R-6  6-ohm  rheostats,  R>  and  RIO,  are 
also  necessary.  A  Carter  M-4OO-S  potentiometer- 
filament  control  switch,  Rg,  is  also  wired  in  the 
circuit.  The  list  of  parts  for  the  a.c.  receiver: 

LIST  OF  PARTS 

Ci,  Q,  Cs — Samson  No.  65  o.oooj-Mfd.  Con- 
densers 122.50 
Li — Samson  No.  71  Antenna  Coil  2.75 
L«,  Li,  Li — Samson  No.  31  Coupler  7.50 
Li.  Le— Samson  No.  41  Oscillator  Coil         2.  85 
Three  Marco  No.  421  Illuminated  Con- 
trols                                                             10.50 
S-M  No.  440  Time  Amplifier  (Includes 
Three  Intermediate  Stages  and  2nd 
Detector) 

T — S-M  No.  220  Audio  Transformer 
LT— S-M  No.  276  Choke  Coil 
Three  S-M  No.  512  Tube  Sockets 
Sw — Yaxley  No.  10  Antenna  Switch 
One  Yaxley  No.  63  Triple-Pole  Switch 
Ri-^-Carter  MW-3ooo  jooo-Ohm  Poten- 
tiometer 

Rz-^-Carter  MW-iooo  lOOO-Ohm  Poten- 
tiometer 

Ra — Carter  MP-2O  20-Ohm  Potentiometer 
RI,  Rt, — Carter  Type  L  5O,ooo-Ohm  "  Hi- 
Ohm" 

Carter  Cathode  Tube  Adapter 
Re — Durham  2-Megohm  Leak 
RT — Frost  FT-64  Mid-Tap  Resistor 
Cf— -Carter  o.oooi5-Mfd.  Grid  Condenser, 

with  Clips 

C6 — Carter  o.oo2-Mfd.  Condenser 
C6 — Carter  No.  210  i-Mfd.  Bypass  Con- 
denser 

Jones  No.  BM  410  Ten-Wire  Cable 
Cortlandt  Panel  7"  x  24"  x  Ta6"  Drilled  and 

Engraved 
Resistor  Mounting  Strip  ij"  x  -j\"  x  -fa" 

Drilled 

Baseboard  12"  x  23"  x  J",  Plywood  Pre- 
ferred 
Two   Rolls  of  "Braidite"   Wire,   Two 

Colors 

One    Fahnestock    Clip    and    Assorted 
Screws 

Total 


35.00 
8.00 
i.oo 

2.25 
.50 
1. 60 

1.25 
1.25 

•75 
4.00 

I.IO 

.50 
.50 

.40 
.50 

1.25 
3-25 

7.50 

i" 

50 

•75 
.60 

70 

$118.25 

The  following  additional  equipment  is  partly 
necessary  to  operate  the  receiver.  A  choice  in 
several  instances  may  be  made  by  the  construc- 
tor. 

Four  c-327  Tubes  £2400 

Three  cx-326  Tubes  9.00 

TI — SM  325  Filament  Transformer  8.00 

One  S-M  660-210  Power  Pack  or —  83.50 

One  S-M  660  171  Power  Pack  66.50 

One  Fritts  Cabinet  7"  x  24"  x  12"  23.50 


HOW    THE    PARTS    ARE    LAID    OUT 

The  coil  units  to  the  left  comprise  Lj,  La, 
LA,   Lt,  and   Le,  while   Li   is   to   the   right 


AS  THE  BROADCASTER  SEES  IT 


Design  and  Operation  of  Broadcasting  Stations 


ig.  Frequency  Runs 

THE  various  elements  of  the  circuits  used 
in  broadcasting  exhibit  effects  which  de- 
pend, among  other  factors,  on  the  fre- 
quency of  the  potentials  applied  to  them.  A 
line,  for  example,  tends  to  attenuate  voice  cur- 
rents of  high  frequency  more  than  currents  of 
lower  frequency,  because  of  the  shunting  ef- 
fect of  the  distributed  capacity,  which  varies 
with  the  frequency.  More  specifically,  we  may 
say  that  every  piece  of  apparatus  has  a  definite 
transmission  characteristic  with  frequency, 
which  it  is  necessary  to  know  if  organizations  of 
apparatus  are  to  be  brought  about  for  given 
objects,  for  example,  impartial  or  "flat"  repro- 
duction of  sounds  of  different  pitches.  Such  a 
curve  of  amplitude  against  frequency  is  secured 
by  means  of  a  frequency  run.  In  broadcasting 
the  most  common  frequency  runs  are  made 
within  the  audio  band,  say  between  50  and 
10,000  cycles  per  second,  and  typical  circuit 


amplitude  of  5-per  cent,  is  allowable,  but  the 
proportion  must  not  be  greater.  The  power  out- 
put of  the  oscillator  should  be  reasonably  con- 
stant over  the  range  of  frequency,  and  it  is  not 
difficult  to  design  an  oscillator  which  will  meet 
this  requirement  within  5  per  cent,  output  volt- 
age variation  over  a  50  to  io,ooo-cycle  band.  The 
oscillator  may  be  one  of  several  types.  One  form 
consists  of  audio  tuned  circuits,  generally  em- 
ploying fixed  condensers  and  obtaining  the  fre- 
quency variation  by  means  of  taps  on  an  iron 
core  coil  of  suitable  inductance.  The  inductance 
and  capacitance  together  tune  to  the  audio  fre- 
quency directly.  Another  type  of  audio  oscillator 
utilizes  the  heterodyne  principle.  Two  radio- 
frequency  oscillators  have  their  outputs  com- 
bined, rectified,  and,  if  necessary,  amplified  at 
audio  frequency.  Generally  one  of  the  compon- 
ent oscillators  has  its  frequency  fixed;  the  other 
radio  frequency  is  varied,  and  the  beats  may  be 
made  to  cover  the  whole  audible  range.  Pre- 
cautions must  be  taken  to  avoid  too  much  fre- 


Repe 
Co 

o 

o 

o 

C2> 

Equalizer 

Audio 
Amplifier 

I 

Volume 

Indicator 

atmg 
I 

500 
ohms 

FIG.    I 


elements  which  require  this  sort  of  investigation 
are  telephone  lines  and  the  audio  circuits  of 
transmitters.  Representative  methods  of  making 
such  tests  will  be  briefly  described  in  this  article. 
Fig.  i  is  a  diagram  showing  how  a  frequency 
run  may  be  made  on  a  wire  line,  using  an  audio 
oscillator  at  the  transmitting  end  and  vacuum- 
tube  voltmeters  for  the  indicating  instruments. 
The  audio  oscillator  in  all  such  work  must  ful- 
fil several  requirements.  It  must  cover  the 
frequency  range  over  which  the  circuit  is  to 
be  equalized.  For  ordinary  line  work,  by  present 
standards,  this  would  be  from  100  to  5000  cycles, 
hence  the  oscillator  of  Fig.  i  will  have  to  more 
than  cover  this  band — a  50  to6ooo-cycle  oscillator 
would  be  suitable.  The  output  must  be  substan- 
tially free  from  harmonics.  Obviously  since  the 
instrument  is  to  be  used  in  determining  fre- 
quency characteristics  one  must  be  able  to  secure 
oscillations  of  any  frequency  in  the  range  with- 
out the  admixture  of  other  frequencies.  If,  for 
example,  the  behavior  of  the  line  is  to  be  studied 
at  200  cycles,  the  harmonics  (400,  600,  800  .  .  . 
cycles)  must  be  suppressed.  Usually  a  harmonic 


quency  drift,  owing  to  varying  voltages,  and  there 
is  also  a  tendency  for  the  two  radio  oscillators 
to  pull  into  synchronism  at  the  lower  beat  fre- 
quencies. Some  information  on  the  construction 
of  audio  beat  oscillators  for  laboratory  testing 
is  contained  in  several  1927  papers  in  the  Pro- 
ceedings of  the  Institute  of  Radio  Engineers 
(Wolff  and  Ringel:  "Loud  Speaker  Testing 
Methods,"  May,  1927;  Dickey:  "Notes  on  the 
Testing  of  Audio-Frequency  Amplifiers,"  Aug- 
ust, 1927;  Diamond  and  Webb:  "Testing  of 
Audio-Frequency  Transformers,"  September, 
1927).  In  general,  broadcasters  who  lack  labora- 


tory training  in  measurements  will  do  better  if 
they  buy  such  instruments  as  audio  oscillators. 
Such  apparatus  is  sold  by  the  General  Radio 
Company,  Graybar  Electric  Company,  and 
other  concerns.  Oscillators  covering  a  range  of 
from  10  to  50,000  cycles,  or  higher,  with  defi- 
nitely known  output  characteristics,  are  obtain- 
able. One  form  covers  from  1 5  to  9000  cycles, 
continuously  variable  through  a  single  control; 
the  price  is  a  little  more  than  $200. 

Returning  now  to  Fig.  I,  we  note  that  the  re- 
ceiving instrument  is  a  "volume  indicator"  of 
the  vacuum-tube  type.  The  circuits  of  a  typical 
form  are  shown  in  Fig.  2.  The  action  will  not  be 
taken  up  in  great  detail,  as  a  previous  article  in 
this  series  ("Volume  Indicators,"  RADIO  BROAD- 
CAST, May,  1927)  dealt  with  the  general  theory. 
In  the  form  shown  the  negative  grid  bias  is  ad- 
justed until  the  d.c.  galvanometer  in  the  plate 
circuit  of  the  tube  reads  5  scale  divisions  out  of 
a  total  of  60  full-scale.  Then  the  tap  on  the 
secondary  of  the  input  transformer  is  set  to  give 
peak  readings,  with  modulation,  of,  say,  30  scale 
divisions.  The  level  of  the  circuit  across  which 
the  instrument  is  bridged  may  then  be  read  on  a 
scale  attached  to  the  transformer  tap  switch. 
High  levels,  obviously,  correspond  to  settings 
in  which  only  a  small  portion  of  the  total  trans- 
former voltage  is  utilized,  whereas  when  the  tele- 
phonic level  is  low,  more  of  the  winding  must  be 
included  by  means  of  the  tap  switch  in  order  to 
get  the  requisite  galvanometer  swing.  Obviously 
the  readings  of  such  an  instrument  are  the  re- 
sultant of  many  factors,  such  as  the  wave  form 
of  the  alternating  currents  under  measure- 
ment, the  ballistic  characteristics  of  the  gal- 
vanometer, the  size  of  the  galvanometer  shunt, 
the  smoothing  characteristics  of  the  inductance- 
capacitance  filter  in  the  plate  circuit,  the  type 
of  vacuum  tube  employed,  and  other  details, 
but  it  is  possible  to  design  such  level  indicators 
to  read  in  telephonic  transmission  units  with 
sufficient  accuracy  for  the  usual  purposes  of 
broadcast  transmission  or  measurement.  The 
prototype  is  the  Western  Electric  518-6  type, 
which,  in  its  lowest  range,  from  minus  m  to 
plus  10  TU,  is  constructed  as  shown  in  Fig. 
2,  but  extends  the  range  of  measurable  levels  to 
as  high  as  plus  40  TU  by  the  addition  of  a  poten- 
tiometer arrangement  across  the  secondary  of 
the  input  transformer. 

Obviously  a  level  indicator  must  always  be  a 
bridging  instrument,  a  circuit  element,  that  is, 
with  a  relatively  high  input  impedance,  intended 
for  connection  across  circuits  of  low  impedance 
without  drawing  enough  energy  from  the  low- 
impedance  circuit  to  affect  conditions  therein. 


MAY,  1928 


AS  THE  BROADCASTER  SEES  IT 


43 


The  volume  indicator  described  above  has  an 
input  impedance  of  about  12,000  ohms  and  it 
must  be  used  across  a  500-  or  6oo-ohm  circuit  if 
its  calibration  is  to  hold.  It  is  so  connected  in' 
the  set-up  for  a  line  frequency  run  shown  in 
Fig.  I.  The  output  of  the  oscillator  is  of  500 
ohms  impedance.  This  feeds  a  IO-TU  artificial 
line  which  presents  an  impedance  of  500  ohms 
in  each  direction.  The  usual  repeating  coil  is 
inserted  ahead  of  the  line.  The  line  is  assumed  to 
have  an  impedance  of  about  500  ohms  also.  At 
the  other  end  of  the  line  there  is  an  equalizer 
(See  article  on  "Types  of  Equalizers,"  RADIO 
BROADCAST,  June,  1026)  followed  by  a  two- 
stage  amplifier,  with  an  output  impedance  of 
500  ohms.  This  amplifier  must  be  terminated 
with  a  resistance  of  this  magnitude,  therefore, 
before  the  level  readings  of  a  volume  indicator 
bridged  across  it  will  be  valid. 

Since  the  equalizer  is  at  the  far  end  of  the 
line,  the  latter  will  not  present  a  strictly  con- 
stant impedance  at  the  transmitting  end,  and 
this  would  affect  the  output  of  the  oscillator  if 
instrument  were  connected  directly  to  the  line. 
The  artificial  line  acts  as  a  buffer,  in  that  it  pro- 
vides a  more  constant  impedance  for  the  oscilla- 
tor to  feed  into;  in  some  cases  the  artificial  line 
network  also  permits  measurement  at  more 
convenient  levels  without  excessive  input  to  the 
telephone  line. 

The  procedure  for  a  frequency  run  is  obvious 
from  this  point  on.  The  oscillator  is  set  at  various 
frequencies,  the  outgoing  level  checked  with  the 
volume  indicator  across  it,  and  similar  readings 
taken  at  the  receiving  end.  A  curve  of  received 
level  against  frequency  may  thus  be  secured  for 
a  given  setting  of  the  equalizer.  If  the  equalizer 
is  omitted,  and  the  transmitted  level  remains 
constant,  such  a  curve  will  show  the  line  attenu- 
ation characteristic,  which  is  a  curve  descending 
with  frequency.  The  object  of  the  equalizer  being 
to  correct  this  loss  of  the  higher  frequencies,  a 
number  of  frequency  runs  may  be  taken,  until 
a  horizontal  curve  of  received  level  is  secured. 
The  line  is  then  equalized.  Communication  be- 
tween the  two  terminals  may  be  maintained  over 
the  line  by  telephone  or  telegraph  in  the  inter- 
vals between  readings,  or  over  a  separate  pair. 
Of  course  before  an  attempt  is  made  to  take  a 
frequency  characteristic  of  a  line,  or  to  set  the 
equalizer  for  a  flat  characteristic,  the  usual  d.c. 
wire  chief's  tests  are  made  for  defects  like  open 
circuits  or  grounds.  Nothing  in  the  way  of  audio- 
frequency testing  can  be  accomplished  until  such 
faults  have  been  eliminated. 

HOW   NOT  TO   DO   IT 

CIG.  3  shows  a  method  of  taking  line  fre- 
quency runs  which  is  illegitimate.  I  have 
seen  it  used,  and  so  mention  it  here  with  the 
caution  that  results  so  secured  will  usually  be 
misleading.  The  oscillator,  with  the  volume  in- 
dicator bridged  across  it,  is  connected  across  a 
500-ohm  resistance  and  the  level  is  read.  The 
output  of  the  oscillator  is  then  switched  to  a 
line,  the  equalizer  being  at  the  other  end.  In 
this  way  a  frequency  run  is  made  and  the  line 
is  thought  to  be  equalized.  Actually,  as  the 
impedance  of  the  line  varies  with  the  frequency, 
the  output  of  the  oscillator  will  also  vary  with 
frequency  and  the  result  of  the  experiment  will 
merely  be  to  show  how  the  oscillator  behaves 
with  a  variable  impedance  connected  across  its 
terminals. 

Sometimes  it  is  convenient  to  send  out  tone 
on  a  line  using  the  regular  broadcast  amplifier 
set-up.  For  example,  in  chain  operation  it  is  a 
sound  precaution  to  transmit  tones  at  a  number 
of  important  frequencies  before  a  program. 
The  network  stations  take  level  readings  at  the 
various  frequencies  transmitted,  which  may  be 


Audio 
Oscillator 

Volume 
Indicator 

FIG.    3 

100,  1000,  and  5000  cycles,  and  telegraph  them 
back  as  a  check  on  the  condition  of  the  lines. 
Any  irregularity  will  show  up  in  these  readings 
and  necessary  changes  in  routing  of  circuits, 
adjustment  of  terminal  apparatus,  etc.,  may  be 
made  before  the  program  begins.  Fig.  4,  from  the 
input  of  the  three-stage  amplifier,  is  the  usual  set- 
up for  broadcasting.  The  input  to  the  first  am- 
plifier would  normally  be  a  microphone.  For  the 
microphone  there  has  been  substituted  the  audio 
oscillator,  a  repeating  coil,  and  a  variable  at- 
tenuation network,  which  can  be  adjusted  to  any 
loss  up  to  30  TU.  By  means  of  this  pad  the 
level  of  the  outgoing  tone  may  be  made  the 
same  as  that  normally  used  during  broadcast- 
ing—usually  around  zero  level  (12  milliwatts  on 
peaks,  or  about  5  milliamperes  into  a  5OO-ohm 
circuit). 

In  the  December,  1924,  issue  of  the  Proceedings 
of  the  Institute  of  Radio  Engineers,  Mr.  Julius 
Weinberger  showed  a  means  of  taking  the  audio- 
frequency characteristic  of  the  modulation  sys- 
tem of  a  radio  station.  The  diagram  is  repro- 
duced, with  some  slight  modifications,  in  Fig. 
5  herewith.  The  audio  oscillator  in  this  case 


Audio 
Oscillator 

Repeating 
Coil 

Variable 
Pad 

3  -Stage 

Audio 
Amplifier 

10  Tu 
Pad 

2  -Stage 

Audio 
Amplifier 

10  Tu 
Pad 

amplitude  compared  with  the  transmission  of 
the  mean  speech  frequency  (1000  cycles),  or  in 
TU,  the  horizontal  axis  representing  frequency. 
The  thermo-galvanometers  in  such  a  set-up 
as  that  shown  in  Fig.  5  must  necessarily  have 
the  right  full-scale  reading  for  the  circuits  under 
measurement.  The  required  capacity  can  readily 
be  calculated,  since  the  output  of  the  oscillator, 
the  amplification  of  the  audio  system,  and  there- 
fore the  alternating  voltage  developed  by  the 
modulators,  will  all  be  approximately  known. 
Where  there  is  any  doubt  a  large  instrument  is 
first  used,  until  one  of  the  right  sensitiveness 
and  current-carrying  capacity  is  found.  As  the 
output  measurements  are  made  across  the  full 
plate  voltage  the  engineer  who  works  on  this 
end  must  take  the  usual  precautions  against 
accidental  contact  with  the  high-tension  por- 
tions of  the  equipment. 

RADIO  FOLK  You  SHOULD  KNOW 
4.  E.  B.  Pilhbury 

[F  THERE  is  a  communication  man  in  the 
'United  States  it  is  Edward  Butler  Pillsbury, 
the  Vice  President  and  General  Manager,  as 
well  as  a  Director,  of  the  Radio  Real  Estate 
Corporation  of  America,  the  holding  company 
for  the  realty  properties  of  the  R.  C.  A.  Mr. 
Pillsbury  has  spent  his  entire  career  in  teleg- 
raphy, starting  as  a  messenger,  working  ten  years 
as  a  Western  Union  operator,  followed  by  many 
years  in  the  service  of  the  Postal  Telegraph- 
Cable  Company,  first  as  Chief  Operator  in  Bos- 


Repeating 
Coil 


FIG.    4 


feeds  into  a  5OO-ohm  resistance,  matching  its 
normal  output  impedance.  A  thermo-galvanom- 
eter  in  series  measures  the  a.c.  emitted  by  the 
oscillator.  A  portion  of  the  voltage  across  the 
500-ohm  resistor  is  fed  into  the  line  amplifier 
of  the  station  with  enough  added  resistance  on 
either  side  to  maintain  the  5OO-ohm  impedance. 
The  tone  passes  through  the  entire  audio-fre- 
quency system  and  the  level  is  measured  at  the 
output  of  the  modulators.  A  fixed  condenser  of 
j-mfd.  capacity  blocks  the  direct  plate  voltage 
and  allows  only  the  audio  component  to  affect 
the  measurement  circuits.  The  lower  terminal 
of  the  condenser  is  connected  to  ground  through 
a  resistance  of  the  order  of  20,000  ohms,  which 
is  so  high  that  the  characteristics  of  the  trans- 
mitter will  be  unaffected  by  the  addition  of 
the  measuring  circuit.  A  relatively  small  portion 
of  the  audio  voltage  across  the  resistor  is  tapped 
off  for  the  thermo-galvanometer.  A  radio- 
frequency  trap  is  usually  required  to  keep  r.f. 
out  of  the  galvanometer  circuit.  The  current 
readings  of  the  input  and  output  galvanometers 
will  now  give  the  transmission  characteristics 
of  the  modulation  system  at  any  frequency 
within  the  compass  of  the  oscillator.  The  curve 
may  be  drawn  with  ordinates  of  percentage  of 


150  ohms 


ton,  then  advancing  to  the  grades  of  local  Man- 
ager in  that  city,  Assistant  Superintendent, 
District  Superintendent  for  New  England,  and 
finally  General  Superintendent  of  the  Eastern 
Division  of  the  company,  with  jurisdiction  over 
the  lines  and  offices  in  thirteen  states  from  his 
headquarters  in  New  York.  This  position 
Mr.  Pillsbury  held  for  six  years,  until  he  re- 
signed to  take  up  radio  work  as  General  Super- 
intendent of  the  Transoceanic  Division  of  the 
Marconi  Wireless  Telegraph  Company  of  Amer- 
ica, and  later  for  the  Radio  Corporation.  In 
1922  he  was  elected  to  his  present  office. 

While  serving  as  an  operator  Mr.  Pillsbury 
was  renowned  as  an  expert  Morse  man.  He  was 
among  the  first  chief  operators  to-adopt  the  prac- 
tice of  using  the  Wheatstone  bridge  method  of 
locating  faults  on  telegraph  lines. 

Anyone  else  who  has  seen  all  he  has  of  the 
communication  business  and  of  life  would  be 
writing  his  memoirs.  But  when  Mr.  Pillsbury 
was  asked  to  supply  information  for  this  bio- 
graphical sketch  he  replied  plaintively.  "  I  re- 
gret to  say  that  no  interesting  anecdotes  or  ex- 
periences have  come  my  way."  Press  agents 
should  thank  God  that  the  country  is  not 
crowded  with  Edward  Butler  Piltsburys. 


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RADIO  BROADCAST  ADVERTISER 


47 


The  Thordarson  Z.-Coupler, 
a  special  audio  impedance 
coupler  for  use  with  screen 
grid  tubes;  price  each,  S12. 


Screen  grid  audio  amplification,  most 
revolutionary  development  in  audio 
systems  since  the  introduction  of  the 
power  tube,  is  now  an  established  fact. 

The  Thordarson  Z-Coupler  is  a  special 
audio  coupling  device  designed  for  use 
with  the  screen  grid  tube  UX-222. 
With    the    remarkable    amplification 
thus  obtained  a  mere  whisper  from  the  t 
detector  is  stepped  up  to  a  point  that 
'gives  the  power  tube  all  it  can  handle 
in  the  way  of  signal  voltage.  In  fact, 
one  stage  Z-Coupled  audio  has  the  am- 
plification equivalent  of  two,  or  even 
three,  stages  of  ordinary  coupling.  Sig- 
nals barely  audible  before  may  now  i 
heard  at  normal  room  volume. 


In  tone  quality,  too,  the  Z-Coupler  is 
unexcelled.  Despite  the  high  amplifi- 
cation the   tonal  reproduction   is  as 
nearly  perfect  as  any  audio  amplifier 
yet  developed.   Both   high  and   low 
notes  come  through  with  the  same  vol- 
ume increase.  Even  at  60  cycles  the 
amplification  is  over  95%  of  maximum. 

Regardless  of  the  type  of  your  receiver 
you  can  vastly  improve  its  perform- 
ance by  including  this  new  system  of 
'  amplification.  The  Z-Coupler  replaces 
the  second  audio  transformer,   with 
very  few  changes  in  the  wiring.  The 
screen  grid  tube  is  used  in  the  first 
audio  stage.  No  shielding  is  required. 


<ov  Complete 
information 


THORDARSON  ELECTRIC  MFG.  CO. 
Huron  and  Kingshury  Sts.,  Chicago,  111. 
Gentlemen : 

Without  obligation  on  my  part,  please  send 
me  complete  information  on  screen  grid  audio 
amplifiers  using  your  new  Z-Coupler.  (3578-J) 


Name 

Street  and  No...- 
Town 


...State. 


RADIO  BROADCAST  ADVERTISER 


orit  use  old 
orlnferiorlubes 
with  New  ones 

Use  new 


throughout 

and  enjoy 

modern  radio 

reception  at 

its  best 

E.T.  CUNNINGHAM,  inc. 

New  York        Ch  i  cago 
San  Francisco 


The  Radio  Broadcast 


SHEETS 


THE  RADIO  BROADCAST  Laboratory  Information  Sheets  are  a  regular  feature  of  this 
magazine  and  have  appeared  since  our  June,  1926,  issue.  They  cover  a  wide  range 
of  information  of  value  to  the  experimenter  and  to  the  technical  radio  man.  It  is  not  our 
purpose  always  to  include  new  information  but  to  present  concise  and  accurate  facts  in 
the  most  convenient  form.  The  sheets  are  arranged  so  that  they  may  be  cut  from  the 
magazine  and  preserved  for  constant  reference,  and  we  suggest  that  each  sheet  be  cut  out 
with  a  razor  blade  and  pasted  on  4"  x  6"  filing  cards,  or  in  a  notebook.  The  cards  should 
be  arranged  in  numerical  order.  In  July,  11527,  an  index  to  all  Sheets  appearing  up  to 
that  time  was  printed.  This  month  we  print  an  index  covering  the  sheets  published  from 
August,  1927,  to  May,  1928,  inclusive. 

All  of  the  1926  issues  of  RADIO  BROADCAST  are  out  of  print.  A  complete 
set  of  Sheets,  Nos.  I  to  88,  can  be  secured  from  the  Circulation  Department, 
Doubleday,  Doran  &  Company,  Inc.,  Garden  City,  New  York,  for  Ji.oo.  Some  readers 
have  asked  what  provision  is  made  to  rectify  possible  errors  in  these  Sheets.  In  the  unfor- 
tunate event  that  any  serious  errors  do  occur,  a  new  Laboratory  Sheet  with  the  old 
number  will  appear 

— THE  EDITOR. 


No.    185 


RADIO  BROADCAST  Laboratory  Information  Sheet 


Tube  Overloading 


May,  1928 


EFFECT  OF  INCORRECT  VOLTAGES 

DURING  recent  years  many  familiar  types  of 
radio  tubes  have  played  the  role  of  "Jack  of 
all  trades,"  and  as  a  result  have  frequently  been 
placed  in  service  under  conditions  never  intended  or 
contemplated  by  the  manufacturer. 

What  constitutes  "overload"  on  a  tube,  re- 
sulting in  shortened  life?  It  might  be  imagined  that 
the  |ast  tube  in  a  receiver  tuned-in  on  a  strong  local 
station,  and  with  the  volume  turned  up  beyond  the 
point  where  the  music  sounds  clear,  would  fall 
under  this  classification,  but  this  is  not  the  case. 
This  is  a  form  of  overloading,  but  one  which  only 
results  in  distorted  music,  and  in  general  the  tube  is 
not  affected  at  all.  A  severe  overload  permanently 
affecting  the  tube  occurs,  however,  when  the  manu- 
facturer s  specifications  as  regards  filament,  plate, 
and  grid  voltages  are  disregarded  and  higher  volt- 
ages are  used. 

One  of  the  popular  tube  types  affords  a  good  illus- 
tration of  this  condition.  The  voltages  recommended 
for  type  201 -A  tubes  area  filament  voltage  of  5.0 


volts,  and  plate  voltages  of  90  to  135  volts,  with  the 
grid  bias  specified  as  -4.5  and  -9.0  volts  respec- 
tively. If  the  grid  bias  of  4.5  volts  recommended  at 
90  volts  is  omitted  it  is  equivalent  to  adding  about 
35  volts  to  the  plate  voltage,  or  in  other  words,  is 
equivalent  to  operation  of  the  tube  at  125  volts 
with -4.5  volts  bias.  The  overload  is,  of  course, 
correspondingly  more  severe  if  the  plate  voltage  is 
raised.  This  is  clearly  shown  in  the  table  below: 


PLATE 
VOLTS 

90 
135 

90 
120 
135 


GRID      CURRENT 


VOLTS 
4.5 
9.0 

0 

0 

0 


MA. 
2.0 
2.5 
6.0 
9.8 

12.0 


EXTENT  OF 
OVERLOAD 
Below  maximum 
Normal 
58% 
240% 
380% 


The  201-A  type  tube  is  capable  of  withstanding 
some  overload  more  successfully  than  other  types 
of  tubes,  but  as  a  general  rule  it  is  always  advisable 
to  follow  the  manufacturer's  ratings  regarding  tube 
voltage. 


No.  186 


RADIO  BROADCAST  Laboratory  Information  Sheet 


The  UX-250  and  CX-350 


May,  1928 


A   NEW   POWER    AMPLIFIER 

THE  ux-250  (cx-350)  is  the  latest  tube  designed 
for  use  as  a  power  amplifier  to  supply  large 
amounts  of  undistorted  power  for  the  operation  of 
loud  speakers.  The  large  output  obtainable  from 
this  tube  prevents  any  possibility  of  overloading 
of  the  last  stage  of  an  audio  amplifier. 

The  filament  rating  is  7.5  volts,  1.25  amperes. 
The  material  used  in  the  filament  is  the  rugged 
coated  ribbon  form,  similar  to  that  used  in  the  ux- 
2bO  (cx-380)  rectifier,  the  filament  operating  at  a 
dull  red.  The  filament  current  may  be  supplied  from 
the  7.5-volt  winding  of  a  power  transformer.  The 
low  operating  temperature  and  the  increased  size 


of  this  type  of  filament  results  in  minimum  ripple 
voltage  or  "hum." 

It  should  be  noted  that,  althougfi  the  filament 
and  plate  voltages  are  the  same  as  those  for  the 
ux-210  (cx-310)  tube,  the  plate  current  is  55  milli- 
amperes  at  a  plate  voltage  of  400  volts  whereas  un- 
der similar  conditions,  the  plate  current  of  the  ux- 
210  (cx-310)  is  only  18  milliamperes.  The  grid 
voltages  for  these  two  tubes,  at  a  plate  voltage  of 
400  volts,  are  respectively  — 70and  —31.5.  the  larger 
voltage  being  necessary  on  the  ux-250  (cx-350) 
tube.  Because  of  the  higher  plate  current  and  grid 
bias  required  by  this  new  tube  it  cannot  always  be 
used  to  replace  the  ux-210  (cx-310)  tube  without 
changing  the  circuit. 


Plate  Voltage 

Negative  Grid  Bias 

Plate  Current 

Plate  Resistance  (a.c.) 

Mutual  Conductance 

Voltage  Amplification  Factor 

Max.  Undistorted  Power  Output 

Filament  7.5  Volts  1 . 25  Amperes 

Max.  Overall  Height  6i"  Diameter  2  IS" 
Base:  Large  Standard  ux  (ex) 


RECOMMENDED 

250  300  350  400 

45  54  63  70 

28  35  45  55 

2100  "2000  1900  1800 

1800  1900  2000  2100 

3.8  38  3.8  3.8 

900  1500  2350  3250 


MAXIMUM 
450     Volts 
84     Volt 
55     Milliamp. 
1800     Ohms 
2100Micromhos 

3.8 
4650    Milliwatts 


RADIO  BROADCAST  ADVERTISER 


49 


N 


|J  IB 


Cle-Ra-Tone  Sockets 


For  Standard  UX  Type 
rf*j-if\  Tubes.  Fc 

fl       \\J\~  easyfindin; 

\}  position  of 

the  prongs. 


Tubes.  For  quick  and 
\gofthe  correct 
position  of  the  tube  and 


toP 


A  new  Five  Prong  Socket 
for  A.  C.  Detector  Tubes. 
Especially  designed  for 
heavy  current -carry  ing 
capacity  for  these  new 
tubes. 


You  can  tell  immediately  into  what  socket  each  tube 
should  go.  No  more  mistakes,  hesitation  or  confusion. 
Improves  the  appearance  of  the  set. 
Cle-Ra-Tone  Sockets  are  spring  supported  to  absorb 
the  shocks  that  distort  tonal  qualities.  The  tube 
"floats"  on  four  finely  tempered  springs,  which  absorb 
shocks  and  jars  from  slamming  doors,  passing  traffic 
and  other  disturbances  caused  by  outside  vibrations. 
One-piece  terminal  to  tube  connection.  Positive  con- 
tacts. Knurled  nuts  for  binding  post  connections  or 
handy  lugs  for  soldering. 

Cle-Ra'Tone  Sockets  have  been  chosen  for  practically 
every  prominent  circuit  for  several  years. 

At  All  Radio  Jobbers  and  Dealers 

Benjamin  Electric  Mfg.  Co. 

12O-128  So.  Sangamon  St.,  Chicago 
247  W.  17th  St.  448  Bryant  St. 

New  York  San   Francisco      r 


§§_>= 


More 
POWER 

From  Your  Eliminator 

If  your  Raytheon 
eliminator  will 
not  hold  its  volt' 
tage  when  sup- 
plying one  or 
two  1?1  or  371 
tubes,  you  can 
probably  bring 
it  back  to  full  voltage  by  the  addi' 
tion  of  an  Aerovox  Condenser  as 
shown.  Here  is  the  circuit.  The 
Condenser  is  a  4  Mfd.  type  402. 


«!/> 


fJtTffl 

f  \t/ 

/    i^.. 
f     *t 

The  Aerovox  "Research  Worker"  contains  much  use- 
ful and  interesting  information,  A  postcard  will 
fiut  your  name  on  the  mailing  list. 


78  WASHINGTON  ST. 
BROOKLYN,  N.  Y. 


4RBORPHONE 

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PRODUCTS 


50 


RADIO  BROADCAST  ADVERTISER 


oAdds   the 
:  Final  Touch 

TABLE  TYPE 


Reg.  U.  S.  Pat.  Off. 


CT'HE  ideal  control  for  volume  and  tone 
J.  of  your  loud-speaker,  from  soft,  sooth- 
ing background  for  conversation,  reading, 
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loud,  crisp,  snappy  entertainment  for  cen- 
ter of  interest.   And  it's  always  at  your 
finger  tips — on  the  end  table,  easy-chair 
arm,  dining  table,  davenport,  sick-room 
table,  telephone  stand — anywhere  for  re- 
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Handsomely  finished  in  statuary  bronze 
and  nickel.  Felt  bottom  to  protect  finest 
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tips  and  connector  block  for  applying  to 
battery  or   socket-power   set,   without 
tools,  skill,  time  or  trouble.  Learn  the 
new  joys  of  controlled  radio!  And  all 
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Ask  your  radio  dealer  to  show  you  the  Table 

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Etiquette".  Or  write  us  direct  for  interesting 

data  on  improving  your  radio. 

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Incorporated 

Specialists  in  Variable  Resistors 
285-7  N.  Sixth  St.,  Brooklyn.  N,  Y. 


Used  Exclusively 
in  the 

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Rayfoto  Receiver 

Approvedby 
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For  Further  Information  Address 

L.S.BRA.CH 

MFG.  COFtR 

ENGINEERS  AND  MANUFACTURERS 

NEWARK.  N  J  u'.S.  A.  TORONTO.  CAN. 


No.  187 


RADIO  BROADCAST  Laboratory  Information  Sheet 


Grid  Bias 


May,  1928 


HOW   TO   CALCULATE    BIAS 


'TMIIS  Laboratory  Information  Sheet  gives  some 
*•  information  regarding  grid  bias  and  how  it 
depends  upon  the  voltage  of  the  grid  battery  and 
the  manner  in  which  the  filament  circuit  of  the 
tube  is  wired. 

The  bias  voltage  on  the  grid  of  a  tube  is  always 
specified  with  respect  to  the  negative  end  of  the 
filament.  In  drawing  A  of  the  diagram  on  Sheet 
No.  188,  the  grid  voltage  is  zero. 

In  drawing  B,  the  filament  resistance  K  has  been 
placed  in  the  negative  leg  of  the  filament,  and  since 
the  drop  across  this  resistance  is  1.0  volt,  the  grid 
bias  is  also  —1.0  volt. 

In  drawing  C,  a  4^-volt  battery  has  been  intro- 
duced in  the  circuit  so  that  the  grid  bias  is  now  equal 
to  the  voltage  of  this  battery  plus  the  voltage  drop 


across  the  resistance  R.  The  bias  is  therefore  —  4J 
plus  -  1.0  or  -5J  volts. 

A  positive  grid  bias  of  +6.0  volts  is  obtained  if 
the  resistance  K  is  connected  in  the  positive  leg  of 
the  filament  and  the  grid  return  is  connected  to  the 
+A  terminal  of  the  battery.  See  sketch  D.  If  the 
grid  return  was  connected  to  the  other  leg  of  the 
resistance,  the  grid  bias  would  be  equal  to  the  volt- 
age drop  in  the  filament  or  4-5.0  volts. 

A  variable  grid  bias  from  —1.0  to  +5.0  volts  can 
be  obtained  by  means  of  the  potentiometer  P  in 
drawing  E.  With  the  potentiometer  at  the  extreme 
left-hand  position,  the  bias  is  — 1.0  volt  (due  to  the 
voltage  drop  in  R)  and  with  the  arm  moved  over 
to  the  extreme  right-hand  position  the  bias  is  +5.0 
volts. 

From  the  information  given  in  this  Sheet  it 
should  be  possible  to  determine  the  grid  bias  with 
any  circuit  arrangement. 


No.  188 


(A) 


RADIO  BROADCAST  Laboratory  Information  Sheet  May,   1928 

Grid  Bias  Calculations 

(B)  (C)  (D)  (E) 


Laboratory  Sheet  No.  187  explains  these  five  circuit  arrangements.  De- 
termination of  the  grid  bias  of  any  circuit  arrangement  is  a  simple  matter 
once  the  information  contained  on  these  sheets  is  mastered 


No.  189 


RADIO  BROADCAST  Laboratory  Information  Sheet 


The  A.  C.  "Universal"  Receiver 


May,  1928 


PARTS    REQUIRED 

T  ABORATORY  Sheet  No.  190  gives  the  circuit 
^-*  of  the  "Universal"  receiver  wired  for  a.c. 
operation.  The  d.c.  receiver  was  described  in  the 
December,  1926,  RADIO  BROADCAST  and  the  circuit 
of  the  d.c.  receiver  was  also  given  on  Laboratory 
Sheet  No.  100,  June,  1927.  The  a.c.  circuit  is  pub- 
lished in  response  to  many  requests  from  readers. 

Li — Antenna  coil  consisting  of  13  turns  of  No.  26 
d.s.c.  wire  wound  at  one  end  of  a  2J-inch  tube. 

La — Secondary  coil  consisting  of  50  turns  of  No. 
26  d.s.c.  wire  wound  on  the  same  tube  as  Li.  The 
separation  between  L!  and  L-j  should  be  i  inch. 

Ls — Primary  of  interstage  coil  constructed  in  same 
manner  as  Li  and  tapped  at  the  exact  center. 

L4 — Secondary  winding  constructed  in  same  man- 
ner as  Lj  and  tapped  at  point  A,  the  15th  turn  from 
that  end  as  L4  which  is  nearest  to  La. 

Ci,  Cj — Two  0.0005-mfd.  variable  condensers. 

Cs — -Neutralizing  condenser,  variable,  0.000015 
mfd. 

C( — Regeneration  condenser,  0.00005  mfd. 


Ls — R.F.  choke  coil,  made  by  winding  400  turns 
of  No.  28  wire  on  J"  dowel. 

Ti,  T! — Two  audio-frequency  transformers. 

R! — Fixed  resistance,  1000  ohms. 

R2,  Rs,  Ri — Center-tapped  resistances  for  a.c. 
tubes. 

R» — Fiied  resistance,  2000  ohms. 

Re — Grid  leak,  2  megohms. 

CB,  Cs — Bypass  condensers,  1-mfd. 

Ci — Grid  condenser,  0.00025-mfd. 

Cs — Output  condenser,  200  volts,  4-mfd. 

LG — Output  choke,  60  henries. 

VT,,  VTa — 226  type  a.c.  tubes. 

VT» — 227  type  a.c.  tube. 

VT, — 171  type  tube. 

Three  standard  four-prong,  sockets. 

One  five-prong  socket. 

Binding  posts. 

C  bias  for  the  tubes  is  obtained  from  resist- 
ances Ri  and  Rs. 

The  227  type  detector  tube  requires  about  30 
seconds  to  heat  up  and  begin  functioning  and  there- 
fore about  this  length  of  time  must  lapse  between 
the  time  the  power  is  turned  on  and  the  set  begins 
to  operate.  The  receiver  must,  of  course,  be  carefully 
neutralized. 


RADIO  BROADCAST  ADVERTISER 


51 


190 


RADIO  BROADCAST  Laboratory  Information  Sheet 


May.  1928 


A  revised  ar- 
rangement of  the 
well-known 
"Universal"  cir- 
cuit which  pro- 
vides for  the  use 
ofa.c.  tubes.  It  is 
fully  described 
on  Labor  atorv 
Sheet  No.  189 


To  Filament  Lighting 
Transformer 


To  6  Power  Unit 


No.    191                        RADIO  BROADCAST  Laboratory  Information  Sheet 

Index 

August,  1927,  to  May,  1928 

May,  1928 

SHEET 
NUMBER  MONTH 

<, 

Glow  Tubes: 

Acoustics 

NUMBER 
166 

MONTH 
February 

How  they  function 
Why  they  are  used 
Grid  Bias 

129 
173 

October 
March 

A  Battery  Chargers 

120 

August 

Calculating  Its  Value 

187 

May 

Audio  Amplifier: 

Why  It  Is  Used 

174 

March 

A.C.  Operated                             148,149 
Frequency  and  load  characteristic  118 

December 
August 

Hertz  Antenna 
Honeycomb  Coils,  Data  on 

121 
130 

September 
October 

General  considerations 

165 

February 

Inductive  Reactance 

139,140 

November 

Resistance-Coupled 

131,132 

October 

Loud  Speakers: 

Transformer  Ratio,  Effect  of 
Capacity,  The  Unit  of 

179 
138 

April 
November 

Exponential  Type 
General  Considerations 

134 
145 

October 
December 

Carrier  Telephony 

136 

October 

Modulated  Oscillator 

164 

February 

Chargers,  A  Battery 
Choke  Coils,  Radio-Frequency 
Condenser  Reactance 
Constant  Frequency  Stations 
Coupled  Circuits 

120 
119 
126,127 
153 
135 

August 
August 
September 
January 
October 

Morse  Code 
Oscillation  Control 
Output  Devices 
Overloading,  Effect  on  Tube 
Power  Supply  Devices: 
Calculation  of  various  toll- 

125 
150 
113 
185 

September 
December 
August 
May 

Ear,  Characteristics  of  the 

168 

February 

ages 

142 

November 

Exponential  Horn,  The 

178 

April 

Care  of 

133 

October 

Fading 
Filter  Choke  Coils 
Filter  Condensers 
Gain,  R.  F.  Amplifiers 

160 
175 
182 
147 

January 
March 
April 
December 

Characteristics     at     various 
voltages 
Desirable  Characteristics 
Transformer    Voltages,    Ef- 
fect of 

146 
128 

180 

December 
September 

April 

No.    192                        RADIO  BROADCAST  Laboratory  Informition  Sheet 

Index  (Continued) 

August,  1927,  to  May,  1928 

May,  1928 

SHEET 

NUMBER 

MONTH 

Radio-Frequency  Choke  Coils 
R.  F.  vs.  A.  F.  Amplification 
Receivers,  Testing  of 

Resonant  Circuits 
Roberts  Reflex,  The 
Selectivity 
Sensitivity 
Single-Control          Receiver, 
Boosting  Sensitivity  of 

SHEET 
NUMBER 

119 
181 
122 
163 
167 
158,159 
170 
170 

151 

MONTH 

August 
April 
September 
February 
February 
January 
March 
March 

December 

Tubes: 
Alternating-Current  Types 
Comparison  of  112  and  171 
Comparison  of  112,  171,  and 
210 
Effect  of  plate  circuit  on  £rid 
circuit 
Parallel  Operation 
171 
112-A 
171-A 
222 
280  and  281 

141 
17.1 

161,162 

176 
137 
123,124 
154 
154 
169 
183 

November 
March 

February 

March 
November 
September 
January 
January 
March 
April 

Solenoid  Coil  Data 

143 

November 

250 

186 

May 

Speech: 

Tuning,  Effect  of  Distributed 

Articulation 
Sources  of  Information  on 

177 
152 

April 
December 

Capacity  on 
"Universal"   Receiver,  A.  C. 

184 

April 

Standard  Frequency  Stations 
Static 
Super-heterodyne,  The 
Transmission  Unit,  The 

153 
116 
117 
114 

January 
August 
August 
August 

Operation  of 
Wavelength-Frequency  Con- 
version 
Wavemeter,  A  Simple 
Wave  Traps 

189,190 

156,157 
172 
155 

May 

January 
March 
January 

145 

December 

115 

August 

Announcing  Dongan 

By-Pass  and  Filter 

Type 

Condensers 

With  the  acquisition  of 
the  business  and  equip- 
ment of  the  Electrical 
Specialties  Mfg.  Company, 
Inc.,  Dongan  now  offers 
the  manufacturers  of  ra- 
dio receivers  a  line  of  fixed 
condensers  comparable  in 
q'uality  and  ingenuity  of 
design  to  Dongan  Radio 
Transformers. 

Mr.  C.  Ringwald,  an  au- 
thority on  condenser  de- 
sign and  construction, 
will  direct  the  condenser 
division  of  the  Dongan 
radio  line. 

Just  as  Dongan  has  pi- 
oneered in  transformer  de- 
velopment, so  will  the 
Dongan  laboratories  strive 
to  maintain  front  rank  in 
fixed  condenser  design. 

Thus  the  radio  industry 
is  assured  additional  per- 
manency in  the  approved 
parts  field. 

Dongan  will  continue  its 
policy  as  an  exclusive 
source  to  set  manufacturers 

—another  Transformer  Success 

To  meet  the  increased  capacity 
of  the  new  UX  250  power  ampli- 
fier tube,  Dongan  engineers  have 
perfected  two  new  Output  Trans- 
formers. No.  1176  is  Push  Pull 
type,  _  No.  1177  a  straight  power 
amplifier  type. 

A  Popular  A  C  Transformer 

No.  6flZ 


Thin  is  one  of  the  be>t-liked  A  C  trans- 
formers on  the  market.  It  is  designed 
to  operate  with  4  UX  226,  1  UY  227  and 
1  UX  171  power  amplifier  tubes. 
Mounted  substantially  in  crystallized 
lacquered  case,  equipped  with  lamp 
cord  and  plug  outlet  for  B-eliminator, 
also  tap  for  control  switch.  $5.75. 

Set  Manufacturer* 
and  Custom  Set  Builders 

will  be  furnished  with  any  desired  in- 
formation   and    engineering 
data     on    request 


DONGAN  ELECTRIC  MFG.  CO. 

2991-3001  Franklin  St.,  Detroit,  Michigan 


VTRANSFORMFHS  of  MERIT  lor  FIFTEEN   YEARS  / 


RADIO  BROADCAST  ADVERTISER 


Model 
528 


Three  Ranges  1 50/8/4  Foils 
for  Testing  A.  C.  Receivers 

For  checking  up  supply  and  tube  voltages — 
a  small,  compact  and  portable  instrument  of 
highest  quality  and  electrical  performance,  yet 
moderate  in  price.  Open  scales,  responsive  and 
excellently  damped.  At  all  dealers  or  write  to: — 

WESTON    ELECTRICAL    INSTRUMENT    CORP. 
604  Frelinghuysen  Ave.  Newark,  N.  J. 

WESTON 

RADIO 
INSTRUMENTS 


Jenkins  £  Adair 
Condenser  Transmitter 


For  Broadcasting,    Phonograph 

Recording,  and 
Power  Speaking  Systems 

THIS  transmitter  is  a  small  condenser  which 
varies  its  capacity  at  voice  frequency,  and 
is  coupled  direct  into  a  single  stage  of  ampli- 
fication, contained  in  the  cast  aluminum  case. 
The  output,  reduced  to  200  ohms,  couples 
to  the  usual  input  amplifier.  The  complete 
transmitter  may  be  mounted  on  the  regulation 
microphone  stand.  It  operates  on  180  v.  B  and 
6  or  12  v.  A  battery. 

This  transmitter  contains  no  carbon,  and  is 
entirely  free  from  background  uoise.  Its  yearly 
upkeep  is  practically  nothing.  It  is  extremely 
rugged,  and  will  withstand  hard  usage. 

Price,  complete  with  20  ft.  shielded  cable, 
$225.00  F.O.B.  Chicago. 

J.  E.  JENKINS  &  S.  E.  ADAIR,  Engineers 

1500  N.  Dearborn  Parkway, 

Chicago,  U.  S.  A. 

Send  for  our  bulletins  on  Broadcasting 
Equipment 


PRESS,  WEATHER,  AND  TIME  SIGNALS 


THE  list  below  has  just  been  released  by  the  Navy 
Department,  radio  service,  to  RADIO  BROADCAST. 
It  includes  the  press,  weather  hydrographic,  and  time 
signals  transmitted  by  United  States  Naval  Stations 
throughout  the  world.  This  list  supersedes  that  ap- 
pearing on  page  514  of  this  magazine  for  March,  1927. 
The  material  in  columns  three  and  four  below  is  of  es- 
pecial interest.  The  abbreviations  employed  and  their 
meaning  follows:  "i.c.w."  interrupted  continuous  wave; 
"c.w.,"  continuous  wave;  "a.c.w.,"  raw  a.c.  These  trans- 


missions are  of  vital  importance  to  all  marine  and  shore 
station  operators.  Other  readers  who  are  interested  in 
listening  to  these  signals  should  employ  a  simple  re- 
generative circuit  with  a  long  antenna.  A  satisfactory 
receiver  for  this  purpose  was  described  on  RADIO 
BROADCAST  Laboratory  Information  Sheet  No.  19, 
August  1926.  Also,  the  article,  "A  Portable  Long- Wave 
Receiver,"  page  166,  RADIO  BROADCAST,  July  1927, 
describes  a  receiver  especially  designed  for  long-wave 
reception. 


TIME 
(GREENWICH 
Civil.) 

STATION 

CALL  SIGN 

FREQUENCY  IN 
KC/S  AND  TYPE 
OF  EMISSION 

MATERIAL  BROADCAST 

0000 

Brownsville,  Tex. 

NAY 

132  i.  c.  w. 

Weather. 

0045 

San  Juan,  P.  R. 

NAU 

48  c.w.      • 

Weather    (1    July   to   15 
November). 

0100 

Norfolk.  Va. 
Puget  Sound,  Wash. 

NAM 
NPC 

122  i.c.w. 
118  c.w. 

Weather 
Weather. 

0115 

Arlington,  Va. 

NAA 

4015  i.c.w. 

Aviation     weather     and 
upper  air  reports. 

0130 

Eureka,  Calif. 
Norfolk,  Va. 

NPW 
NAM 

104  i.c.w. 
122  i.c.w. 

Weather,  hydrographic. 
Weather. 

0200 

Cavite,  P.  I. 
Guantanamo  Bay,  Cuba. 

San  Juan,  P.  R. 

NPO 
NAW 

NAU 

56  c.w.  &  112  i.c.w. 
118  i.c.w. 

106  i.c.w. 

Press. 
Weather   (1   June  to  15 
November). 
Weather   (1   July  to  15 
November)  . 

0255  to  0300 

Arlington.  Va. 

Annapolis,  Md. 
Cavite,  P.  I. 

NAA 

NSS 
NPO 

112  i.c.w. 
690  i.c.w. 
4015  i.c.w. 
8030  i.c.w. 
12045  i.c.w. 
17.6  c.w. 
56  c.w. 
112  i.c.w. 

Time  Signals. 

Time  Signals. 
Time  Signals. 

0300 

Arlington,  Va. 

Cavite,  P.  I. 

Key  West,  Fla. 
Puget  Sound,  Wash. 

NAA 

NPO 

NAR 
NPC 

36  c.w. 
112  i.c.w. 

56  c.w. 
112  i.c.w. 
102  i.c.w. 
118  c.w. 

Marine  Weather  fotlou-ed 
by    Navigational    Warn- 
ings and  ice  reports  (in 
season). 
Weather,  hydrographic. 

Weather,  hydrographic. 
Hydrographic. 

0305 

Navy  Yard,  Wash.  D.  C. 

NAA 

690  voice 

Weather. 

0330 

San  Francisco,  Calif. 
Tutuila,  Samoa 

NPG 
NPU 

42.8  c.w. 
108  i.c.w. 
66  c.w. 

Weather,  hydrographic. 
Hydrographic. 

0355  to  0400 

Balboa,  C.  Z. 
Colon,  C.  Z. 

NBA 
NAX 

46  c.w. 
132  i.c.w. 

Time  Signals. 
Time  Signals. 

0400 

Arlington,  Va. 

Great  Lakes,  111. 
Puget  Sound,  Wash. 
San  Juan,  P.  R. 

NAA 

NAJ 
NPC 
NAU 

4015  i.c.w. 

132  i.c.w. 

118  c.w. 
48  c.w. 

Weather      broadcast      to 
Europe. 
Weather,  hydrographic. 
Weather. 
Weather. 

0430 

Astoria,  Oreg. 
San  Diego,  Calif. 

NPE 
NPL 

112  i.c.w. 
102  i.c.w. 

Hydrographic. 
Weather. 

0500 

Brownsville,  Tex. 

NAY 

132  i.c.w. 

Weather. 

0555  to  0600 

San  Francisco,  Calif. 

NPG 

42.8  c.w. 
62  c.w. 
108  i.c.w. 

Time  Signals. 

0600 

San  Francisco,  Calif. 

NPG 

108  i.c.w. 

Weather,  hydrographic. 

0630 

Honolulu,  T.  H. 

NPM 

54  a.c.w. 

Weather,  hydrographic. 

0700 

Annapolis,  Md. 
Arlington,  Va. 

NSS 
NAA 

17.6  c.w. 
112  i.c.w. 

Press. 
Press. 

0730 

Tutuila,  Samoa 

NPU 

66  c.w. 

Hydrographic. 

1000 

Balboa,  C.  Z. 
Balboa,  C.  Z. 
Colon,  C.  Z. 
San  Diego,  Calif. 

NBA 
NBA 
NAX 
NPL 

46  c.w. 
118  c.w. 
132  i.c.w. 
30.6  c.w. 

Press  and  hydrographic. 
Press. 
Hydrographic. 
Press. 

1300 

Puget  Sound,  Wash. 

NPC 

118  c.w. 

Weather. 

1315 

Arlington,  Va. 

NAA 

4015  i.c.w. 
8030  i.c.w. 
12045  i.c.w. 

Aviation     weather     and 
upper  air  reports. 

1330 

Norfolk,  Va. 

NAM 

122  i.c.w. 

Weather. 

1355  to  1400 

Cavite,  P.  I. 

NPO 

56  c.w. 
112  i.c.w. 

Time  Signals. 

1400 

Cavite,  P.  I. 

NPO 

56  c.w. 
112  i.c.w. 

Weather,  hydrographic. 

1500 

Arlington,  Va. 

NAA 

112  i.c.w. 
16060  i.c.w. 

Marine  weather  followed 
by  ice  reports  (in  season)  . 

1505 

Arlington,  Va. 

NAA 

690  voice 

Weather. 

RADIO  BROADCAST  ADVERTISER 


53 


PRESS,  WEATHER,  AND  TIME  SIGNALS 

(Continued) 


A   TIME  CONVERSION  TABLE 


TIME 
(GREENWICH 
CIVIL) 

STATION 

CALL  SIGN 

FREQUENCY  IN 
KC/S  AND  TYPE 
OK  EMISSION 

MATERIAL  BROADCAST 

IfviO 

New  York,  N.  Y. 
Charleston,  S.  C. 

NAH 

NAO 

108  i.c.w. 
122  i.c.w. 

Weather,  hydrographic. 
Weathe-r,  hydrographic. 

1545 

Philadelphia,  Pa. 
Great  Lakes,  111. 
Norfolk,  Va. 

NAI 
NAJ 
NAM 

104  i.c.w. 
132  i.c.w. 
122  i.c.w. 

Weather,  hydrographic. 
Weather,  hydrographic. 
Weather,  hydrographic. 

1600 

Boston,  Mass. 
Newport,  R.  I. 
Arlington,  Va. 

New  Orleans,  La. 
San  Juan,  P.  R. 
Savannah,  Ga. 

NAD 

NAF 
NAA 

NAT 
NAU 
NEV 

102  i.c.w. 
118  i.c.w. 
12045  i.c.w. 

106  c.w. 
48  c.w. 
132  i.c.w. 

Weather,  hydrographic. 
Weather,  hydrographic. 
Weather      broadcast      to 
Europe. 
Weather,  hvdrographic. 
Weather. 
Weather. 

1630 

Jupiter,  Fla. 
San  Diego,  Calif. 
St.  Augustine,  Fla. 

NAQ 
NPL 
NAP 

132  i.c.w. 
102  i.c.w. 
128  spark 

Weather. 
Weather. 
Weather. 

1645 

Pensacola,  Fla. 

NAS 

112  i.c.w. 

Weather. 

1655  to  1700 

Arlington,  Va. 

Annapolis,  Md. 
Great  Lakes,  111. 
Key  West,  Fla. 
New  Orleans,  La. 
San  Diego,  Calif. 

NAA 

NSS 
NAJ 
NAR 
NAT 
NPL 

112  i.c.w. 
690  i.c.w. 
4015  i.c.w. 
8030  i.c.w. 
12045  i.c.w. 
17.6  c.w. 
132  i.c.w. 
102  i.c.w. 
106  c.w. 
30.6  c.w. 
102  i.c.w. 

Time  Signals. 

Time  Signals 
Time  Signals 
Time  Signals 
Time  Signals 
Time  Signals 

1700 

Arlington,  Va. 
Brownsville,  Tex. 
Eureka.  Calif. 
Key  West,  Fla. 
Puget  Sound,  Wash. 
San  Francisco,  Calif. 

NAA 
NAY 
NPW 
NAR 
NPC 
NPG 

112  i.c.w. 
132  i.c.w. 
104  i.c.w. 
102  i.c.w. 
118  c.w. 
42.8  c.w. 

Navigational  warnings. 
Weather. 
Weather,  hydrographic. 
Weather,  hydrographic. 
Weather,  hydrographic. 
Weather,  hydrographic. 

1755  to  1800 

Balboa,  C.  Z. 
Colon,  C.  Z. 

NBA 
NAX 

46  c.w. 
132  spark 

Time  Signals. 
Time  Signals. 

1800 

Balboa,  C.  Z. 

NBA 

46  c.w. 

Hydrographic. 

1830 

Honolulu,  T.  H. 

NPM 

54  a.  c.w. 

Weather,  hydrographic. 

1930 

Tutuila,  Samoa 

NPU 

66  c.w. 

Hydrographic. 

1955  to  2000 

Astoria,  Oreg. 
Eureka,  Calif. 
San  Francisco,  Calif. 

NPE 
NPW 
NPG 

112  i.c.w. 
104  i.c.w. 
42.8  c.w. 
62  c.w. 
108  c.w. 

Time  Signals. 
Time  Signals. 
Time  Signals. 

2045 

Arlington,  Va. 

NAA 

690  voice 

Weather. 

2100 

Norfolk,  Va. 
Puget  Sound,  Wash. 

NAM 

NPC 

122  i.c.w. 
118  c.w. 

Weather,  hydrographic. 
Weather,  hydrographic. 

2130 

Astoria,  Oreg. 

NPE 

112  i.c.w. 

Hydrographic. 

2200 

Boston,  Mass. 
Newport,  R.  I. 
New  York.  N.  Y. 
Phila.  Pa. 
Annapolis,  Md. 
Eureka,  Calif. 
Great  Lakes,  111. 
New  Orleans,  La. 
San  Diego,  Calif. 

NAD 
NAF 
NAH 
NAI 
NSS 
NPW 
NAJ 
NAT 
NPL 

102  i.c.w 
118  i.c.w 
108  i.c.w 
101  i.c.w 
17.6  c.w. 
1O1  i.c.w 
132  i.c.w 
106  c.w. 
102  i.c.w. 

Weather,  hydrographic. 
Weather,  hydrographic. 
Weather,  hvdrographic. 
Weather,  hydrographic. 
Ice  reports  (in  season). 
Weather,  hydrographic. 
Hydrographic. 
Weather,  hvdrographic. 
Weather. 

2230 

Honolulu,  T.  H. 

NPM 

54  a.  c.w. 

Weather,  hvdrographic. 

2300 

Charleston,  S.  C. 
Jupiter,  Fla. 
Pensacola,  Fla. 
Savannah,  Ga. 

NAO 
NAQ 

NAS 
NEV 

122  i.c.w. 
132  a.c.w. 
112  i.c.w. 
132  i.c.w. 

Weather,  hvdrographic. 
Weather. 
Weather. 
Weather. 

2330 

Tutuila,  Samoa 

NPU 

66  c.w. 

Hydrographic. 

2355  to  2400 

Honolulu,  T.  H. 

NPM 

26.  i.c.w. 
106  i.c.w. 

Time  signals. 

/^REENWICH  Mean  Time  was  adopted 
VJ  by  the  recent  International  Radio  Tele- 
graph Convention  in  Washington  for  use  in 
the  Convention  and  regulations  drawn  up  by 
it.  Greenwich  Civil  Time  is  used  in  the  Navy 
for  navigation  and  that  time  is  employed  in 
naval  almanacs.  The  conversion  table  below 
indicates  the  relation  between  G.C.T.,  G.M.T.. 
and  75th  Meridian  Time.  The  latter  is  "East- 
ern Standard"  Time  and  those  living  in  other 


time  belts  can  easily  calculate  the  time  to  listen 
for  these  transmissions  in  their  own  locality. 


G.C.T. 

(Hours) 

0 

6 

12 

14 

18 

22 

24 


G.M.T. 
(Hours) 
12 
18 
0 
2 
6 
10 
12 


75TH  MERIDIAN 

7.00  p.m. 
1.00p.m. 
7.00  p.m. 
9.00  p.m. 
1.00p.m. 
5.00  p.m. 
7.00  p.m. 


Electrify  Your  Set 


WITH  THE 


MARATHON 

JICK1T 

SIMPLE  AS  A-B-C 


Marathon  AC  Tubes 
have  the  standard  4 
prong  UX  bases.  No 
adaptors  or  center  tap 


Replace  i|our  old  Tubes 
with  Marafhon  A-CTubes 


The  Marathon  harness 
is  universal,  and  can  be 
used  in  any  set.  The 
"spades"  slip  over  the 
projections  on  the  tube 
— no  thumb  screws. 


Connect  the  harness 


One  end  of  the  harness 
connects  with  the 
Marathon  Trans- 
former. All  tubss  oper- 
ate on  one  voltage — 6 
volts  —  so  there  are  no 


in  the  Unfit  tcrlef  ^ps.  Simply  plug  the 

Ml  IIIC  IICJIII  WCBer    transformer    Into    the 

that's  all  there  istodo  light  80cket' 

YOU  CAN'T  MAKE  IT 
COMPLICATED 


No  need  to  wonder  if 
the  Marathon  AC  Kit 
will  operate  on  your  set 
— we   guarantee    it.    If 
you  have  a  5,  6,  7  or  8 
tube   set  using  UX 
sockets    and   are    now 
employing  an  **A"  Bat- 
tery (either  dry  cell  or 
storage)    you    can    use 
the  Marathon  A  C  Kit — perfectly. 
Marathon  AC  Tubes  are  guaran- 
teed for  a  year.    If  your  dealer 
cannot  supply  you  use  the  cou- 
pon below. 

The  Marathon  AC  Kit 

is  Complete 

Nothing  else  to  buy — everything 
Is  complete.  For  example  the  six 
tube  kit  includes  6  Marathon  AC  Tubes — a  uni- 


Jobbers^— Dealers 

Write  or  wire  for  our  sales  proposition.  You  can  ab- 
solutely guarantee  the  operation  of  the  Marathon 
AC  Kit. 

NORTHERN  MFG.  CO. 

NEWARK,  NEW  JERSEY 


Northern  Manufacturing  Co., 

376  Ogden  St.,  Newark,  N.  J. 
Send  me  complete   information   on   the 
Marathon  AC  Kit. 

Jobber Dealer 

Professional  Builder 1  »,-r 

(Please  check  your  claaification) 

Name 

Address 


RADIO  BROADCAST  ADVERTISER 


New  Aero  Circuits 

for  Either  Battery  or  A.  C.  Operation 

Proper  constants  for  A.  C.  operation  of  the  Im- 
proved Aero-Dyne  6  and  the  Aero  Seven  have  been 
studied  out,  and  these  excellent  circuits  are  now 
adaptable  to  either  A.  C.  or  battery  operation.  A.  C. 
blue  prints  are  packed  in  foundation  units.  They 
may  also  be  obtained  by  sending  asc  for  each  direct 
to  the  factory. 


Aero  Universal 
Tuned  Radio  Frequency  Kit 

Especially  designed  for  the  Improved  Aero-Dyne  6. 
Kit  consists  of  4  twice-matched  units.  Adaptable  to 
20I-A,  ipg,  112,  and  the  new  240  and  A.  C.  Tubes. 
Tuning  range  below  200  to  above  550  meters. 

Code  No.  U-16  (for  .0005  Cond.) $15.00 

Code  No.  U-163  (for  .00035  Cond.) 15.00 


Aero  Seven 
Tuned  Radio  Frequency  Kit 

Especially  designed  for  the  Aero  7.    Kit  consists 
of  3  twice-matched  units.  Coils  are  wound  on  Bake- 
lite  skeleton  forms,  assuring  a  95  per  cent,  air  dielec- 
tric.   Tuning  range  from  below  200  to  above  550 
meters.    Adaptable  to  aio-A,  199,  112,  and  the  new 
240  and  A.  C.  Tubes. 
Code  No.  U-12  (for  .0005  Cond.)...  ...$12.00 

Code  No.  U-123  (for  .00035  Cond.) 12.00 

You  ihtmld  be  able  to  get  any  of  the  above 

Aero  Coil*  and  part*  from  your  dealer. 

If  he  should  be  out  of  stock  order 

direct  from  the  factory. 

AERO  PRODUCTS,  INC. 

1772  Wilson  Ave.       Dept.  109       Chicago,  III. 


Flexible  A.  C. 
Superheterodyne 

An  aristocrat  of  a  famous  family  espec- 
ially designed  to  meet  the  demands  of  that 
select  circle  of  set  builders  who  desire  the 
finest  in  receiver  construction  with  cost  a 
secondary  consideration. 

Complete  detailed  blueprints  on  this 
unique  combination  of  the  best  radio  prin- 
ciples, $1.00  postpaid.  All  specified  parts 
supplied.  Price  list  on  request. 

DANA  ADAMS 

222  East  52nd  St.  N.  Y.  City 

Western  Office:  6O4  Davis  St.,  Evaiuton,  III. 


Radio 

Convenience 
Outlets 

Wire  your  home  for  radio.  These  out- 
lets fit  any  standard  switch  box.  Full 
instructions  with  each  outlet. 

No.  135— For  Loud  Speaker Sl.OO 

No.  137 — For  Battery  Connections  2.50 
No.  136  For  Aerial  and  Ground  1.00 

With  Bakelite  Plate* 

Now  furnished  with  a  rich  satin  brown  Bakelite 
plate,  with  beautiful  markings  to  harmonize,  at 
25  cents  extra.    See  Illustration. 
At  Your  Dealers 

Yaxley    Mfg.    Company 

Depl.  B,  9  So.  Clinton  St. 
Chicago.   III. 


A  Varied  List  of  Books  Pertaining  to  Radio  and  Allied 
Subjects  Obtainable  Free  With  the  Accompanying  Coupon 


?  may  obtain  any  of  tbe  booklets  listed  below  by  use- 
'^-  ing  tbe  coupon  printed  on  page  57.  Order  by  number  only. 

1.  FILAMENT  CONTROL — Problems  of  filament  supply, 
voltage  regulation,  and  effect  on  various  circuits.  RADIALL 
COMPANY. 

2.  HARD  RUBBER  PANELS — Characteristics  and  proper- 
ties of  hard  rubber  as  used  in  radio,  with  suggestions  on 
how  to  "work"  it.  B.  F.  GOODRICH  RUBBER  COMPANY. 

3.  TRANSFORMERS — A  booklet  giving  data  on  input  and 
output  transformers.  PACENT  ELECTRIC  COMPANY. 

5.  CARBORUNDUM  IN  RADIO — A  book  giving  pertinent 
data  on  the  crystal  as  used  for  detection,  with  hook-ups, 
and  a  section  giving  information  on  the  use  of  resistors. 
THE  CARBORUNDUM  COMPANY. 

7.  TRANSFORMER  AND  CHOKE-COUPLED  AMPLIFICA- 
TION—Circuit  diagrams  and  discussion.  ALL-AMERICAN 
RADIO  CORPORATION. 

9.  VOLUME  CONTROL — A  leaflet  showing  circuits  for 
distortionless  control  of  volume.  CENTRAL  RADIO  LABORA- 
TORIES. 

10.  VARIABLE  RESISTANCE — As  used  in  various  circuits. 
CENTRAL  RADIO  LABORATORIES. 

it.  RESISTANCE  COUPLING — Resistors  and  their  ap- 
plication to  audio  amplification,  with  circuit  diagrams. 
UEjuR  PRODUCTS  COMPANY. 

12.  DISTORTION  AND  WHAT  CAUSES  IT — Hook-ups  of 
resistance-coupled  amplifiers  with  standard  circuits.  ALLEN- 
BRADLEY  COMPANY. 

1 5.  B-ELIMINATOR    AND    POWER    AMPLIFIER — Instruc- 
tions for  assembly  and  operation  using   Raytheon  tube. 
GENERAL  RADIO  COMPANY. 

153.  B-ELIMINATOR  AND  POWER  AMPLIFIER — Instruc- 
tions for  assembly  and  operation  using  an  R.  C.  A.  rectifier. 
GENERAL  RADIO  COMPANY. 

16.  VARIABLE  CONDENSERS — A  description  of  the  func- 
tions and  characteristics  of  variable  condensers  with  curves 
and  specifications  for  their  application  to  complete  receivers. 
ALLEN  D.  CARDWELL  MANUFACTURING  COMPANY. 

17.  BAKELITE — A  description  of  various  uses  of  bakelite 
in  radio,  its  manufacture,  and  its  properties.   BAKELITE 
CORPORATION. 

20.  AUDIO  AMPLIFICATION — A  booklet  containing  data 
on  audio  amplification  together  with  hints  for  the  construc- 
tor. ALL  AMERICAN  RADIO  CORPORATION. 

21.  HIGH-FREQUENCY  DRIVER  AND  SHORT-WAVE  WAVE- 
METER — Constructional    data    and    application.    BURGESS 
BATTERY  COMPANY. 

46.  AUDIO-FREQUENCY   CHOKES — A   pamphlet   showing 
positions  in  the  circuit  where  audio-frequency  chokes  may 
be  used.  SAMSON  ELECTRIC  COMPANY. 

47.  RADIO-FREQUENCY    CHOKES — Circuit    diagrams    il- 
lustrating the  use  of  chokes  to  keep  out  radio- frequency 
currents  from  definite  points.  SAMSON  ELECTRIC  COMPANY. 

48.  TRANSFORMER  AND  IMPEDANCE  DATA — Tables  giving 
the  mechanical  and  electrical  characteristics  of  transformers 
and  impedances,  together  with  a  short  description  of  their 
use  in  the  circuit.  SAMSON  ELECTRIC  COMPANY. 

49.  BYPASS  CONDENSERS — A  description  of  the  manu- 
facture of  bypass  and  filter  condensers.  LESLIE  F.  MUTER 
COMPANY. 

50.  AUDIO   MANUAL — Fifty   questions  which  are  often 
asked   regarding  audio  amplification,   and   their  answers. 
AMERTRAN  SALES  COMPANY,  INCORPORATED. 

51.  SHORT-WAVE  RECEIVER— Constructional  data  on  a 
receiver  which,  by  the  substitution  of  various  coils,  may  be 
made  to  tune  from  a  frequency  of  16,660  kc.  (18  meters)  to 
1999  kc.  (150  meters).  SILVER-MARSHALL,  INCORPORATED. 

52.  AUDIO  QUALITY — A  booklet  dealing  with  audio-fre- 
quency amplification  of  various  kinds  and  the  application 
to  well-known  circuits.  SILVER-MARSHALL.  INCORPORATED. 

56.  VARIABLE     CONDENSERS — A     bulletin     giving     an 
analysis  of  various  condensers  together  with  their  charac- 
teristics. GENERAL  RADIO  COMPANY. 

57.  FILTER   DATA— Facts  about   the  filtering  of  direct 
current  supplied  by  means  of  motor-generator  outfits  used 
with  transmitters.  ELECTRIC  SPECIALTY  COMPANY. 

59.  RESISTANCE  COUPLING — A  booklet  giving  some 
general  information  on  the  subject  of  radio  and  the  applica- 
tion of  resistors  to  a  circuit.  DAVEN  RADIO  CORPORATION 

62.  RADio-FREguFNcv    AMPLIFICATION — Constructional 
details  of  a  five-tube  icceiver  using  a  special  design  of  radio- 
frequency  transformer.  CAMFIELD  RADIO  MFG.  COMPANY. 

63.  FIVE-TUBE      RECEIVER— Constructional     data     on 
building  a  receiver.  AERO  PRODUCTS,  INCORPORATED. 

66.  SUPER-HETERODYNE — Constructional  details  of  a 
seven-tube  set.  G.  C.  EVANS  COMPANY. 

70.  IMPROVING  THE  AUDIO  AMPLIFIER — Data  on  the 
characteristics  of  audio  transformers,  with  a  circuit  diagram 
showing  where  chokes,  resistors,  and  condensers  can  be  used. 
AMERICAN  TRANSFORMER  COMPANY. 

72.  PLATE  SUPPLY  SYSTEM — A  wiring  diagram  and  lay- 
out plan  for  a  plate  supply  system  to  be  used  with  a  power 
amplifier.  Complete  directions  for  wiring  are  given.  AMER- 
TRAN SALES  COMPANY. 

80.  FIVE-TUBE  RECEIVER — Data  are  given  for  the  con- 
struction of  a   five-tube   tuned    radio-frequency   receiver. 
Complete  instructions,  list  of  parts,  circuit  diagram,  and 
template  are  given.  ALL-AMERICAN  RADIO  CORPORATION. 

81.  BETTER  TUNING — A  booklet  giving  much  general  in- 
formation on  the  subject  of  radio  reception  with  specific  il- 
lustrations. Primarily  for  the  non-technical  home  construc- 
tor. BREMER-TULLY  MANUFACTURING  COMPANY. 

82.  SIX-TUBE  RECEIVER— A  booklet  containing  photo- 
graphs, instructions,  and  diagrams  for  building  a  six-tube 
shielded  receiver.  SILVER-MARSHALL,  INCORPORATED. 

83.  SOCKET  POWER  DEVICE — A  list  of  parts,  diagrams, 
and  templates  for  the  construction  and  assembly  of  socket 
power  devices.  JEFFERSON  ELECTRIC  MANUFACTURING  COM- 
PANY. 

84.  FIVE-TUBE   EQUAMATIC — Panel  layout,  circuit  dia- 
grams, and  instructions  for  building  a  five-tube  receiver,  to- 
gether with  data  on  the  operation  of  tuned  radio-frequency 
transformers  of  special  design.  KARAS  ELECTRIC  COMPANY, 


85.  FILTER — Data  on  a  high-capacity  electrolytic  con- 
denser used  in  filter  circuits  in  connection  with  A  socket 
power  supply  units,  are  given  in  a  pamphlet.  THE  ABOX 
COMPANY. 

86.  SHORT-WAVE  RECEIVER — A  booklet  containing  data 
on  a  short-wave  receiver  as  constructed  for  experimental 
purposes.    THE    ALLEN    D.    CARDWELL    MANUFACTURING 
CORPORATION. 

88.  SUPER-HETERODYNE  CONSTRUCTION — A  booklet  giv- 
ing full  instructions,  together  with  a  blue  print  and  necessary 
data,  for  building  an  eight-tube  receiver.  THE  GEORGE  W. 
WALKER  COMPANY. 

89.  SHORT-WAVE  TRANSMITTER— Data  and  blue  prints 
are  given  on  the  construction  of  a  short-wave  transmitter,. 
together  with  operating  instructions,  methods  of  keying,  and 
other  pertinent  data.  RADIO  ENGINEERING  LABORATORIES. 

90.  IMPEDANCE  AMPLIFICATION — The  theory  and  practice 
of  a  special  type  of  dual-impedance  audio  amplification  are 
given.  ALDEN  MANUFACTURING  COMPANY. 

93.  B-SOCKET  POWER— A  booklet  giving  constructional 
details  of  a  socket-power  device  using  either  the  BH  or  313. 
type  rectifier.  NATIONAL  COMPANY,  INCORPORATED. 

94  POWER  AMPLIFIER — Constructional  data  and  wiring. 
diagrams  of  a  power  amplifier  combined  with  a  B-supply 
unit  are  given.  NATIONAL  COMPANY,  INCORPORATED. 

too.  A,  B,  AND  C  SOCKET-POWER  SUPPLY — A  booklet 
giving  data  on  the  construction  and  operation  of  a  socket 
power  supply  using  the  new  high-current  rectifier  tube. 
THE  Q.  R.  S.  Music  COMPANY. 

101.  USING  CHOKES — A  folder  with  circuit  diagrams  of 
the  more  popular  circuits  showing  where  choke  coils  may 
be  placed   to  produce  better    results.  SAMSON   ELECTRIC 
COMPANY. 

22.  A     PRIMER     OF     ELECTRICITY — Fundamentals     of 
electricity  with  special  reference  to  the  application  of  dry 
cells  to  radio  and  other  uses.  Constructional  data  on  buzzers, 
automatic  switches,  alarms,  etc.  NATIONAL  CARBON  COM- 
PANY. 

23.  AUTOMATIC    RELAY    CONNECTIONS — A    data    sheet 
showing  how  a  relay  may  be  used  to  control  A  and  B  cir- 
cuits. YAXLEY  MANUFACTURING  COMPANY. 

26.  DRY     CELLS     FOR     TRANSMITTERS — Actual     tests 
given,  well  illustrated  with  curves  showing  exactly  what 
may  be  expected  of  this  type  of  B  power.  BURGESS  BATTERY 
COMPANY. 

27.  DRY-CELL  BATTERY  CAPACITIES  FOR  RADIO  TRANS- 
MITTERS— Characteristic  curves  and  data  on  discharge  tests. 
BURGESS  BATTERY  COMPANY. 

28.  B  BATTERY  LIFE — Battery  life  curves  with  general 
curves  on  tube  characteristics.   BURGESS  BATTERY  COM- 
PANY. 

30.  TUBE  CHARACTERISTICS — A  data  sheet  giving  con- 
stants of  tubes.  C.  E.  MANUFACTURING  COMPANY. 

32.  METERS  FOR  RADIO — A  catalogue  of  meters  used  in 
radio,  with  diagrams.   BURTON-ROGERS  COMPANY. 

33.  SWITCHBOARD  AND  PORTABLE   METERS — A  booklet 
giving  dimensions,   specifications,   and   shunts   used   with 
various  meters.  BURTON-ROGERS  COMPANY. 

35.  STORAGE      BATTERY      OPERATION — An     illustrated 
booklet  on  the  care  and  operation  of  the  storage  battery. 
GENERAL  LEAD  BATTERIES  COMPANY. 

36.  CHARGING  A  AND  B  BATTERIES — Various   ways   of 
connecting  up  batteries  for  charging  purposes.  WESTING- 
HOUSE  UNION  BATTERY  COMPANY. 

37.  WHY  RADIO  Is  BETTER  WITH  BATTERY  POWER — Ad- 
vice on  what  dry  cell  battery  to  use;  their  application  to 
radio,  with  wiring  diagrams.  NATIONAL  CARBON  COMPANY. 

53.  TUBE  REACTIVATOR — Information  on  the  care  of 
vacuum  tubes,  with  notes  on  how  and  when  they  should  be 
reactivated.  THE  STERLING  MANUFACTURING  COMPANY. 

69.  VACUUM  TUBES— A  booklet  giving  the  characteris- 
tics of  the  various  tube  types  with  a  short  description  of 
where  they  may  be  used  in  the  circuit.  RADIO  CORPORA- 
TION OF  AMERICA. 

77.  TUBES — A  booklet  for  the  beginner  who  is  interested 
in  vacuum  tubes.  A  non-technical  consideration  of  the 
various  elements  in  the  tube  as  well  as  their  position  in  the 
receiver.  CLEARTRON  VACUUM  TUBE  COMPANY. 

87.  TUBE  TESTER — A  complete  description  of  how  to 
build  and  how  to  operate  a  tube  tester.  BURTON-ROGERS 
COMPANY. 

91.  VACUUM  TUBES — A  booklet  giving  the  characteristics 
and  uses  of  various  types  of  tubes.  This  booklet  may  be 
obtained  in   English,  Spanish,  or  Portuguese.   DEFOREST 
RADIO  COMPANY. 

92.  RESISTORS   FOR   A.    C.   OPERATED    RECEIVERS — A 
booklet  giving  circuit  suggestions  for  building  a.  c.  operated 
receivers,  together  with  a  diagram  of  the  circuit  used  with 
the  new  4OO-milIiampere  rectifier    tube.    CARTER   RADIO 
COMPANY. 

102.  RADIO  POWER  BULLETINS — Circuit  diagrams,  theory 
constants,  and  trouble-shooting  hints  for  units  employing 
the  BH  or  B  rectifier  tubes.  RAYTHEON  MANUFACTURING 
COMPANY. 

103.  A.  C.  TUBES — The  design  and  operating  character- 
istics of  a  new  a.  c.  tube.  Five  circuit  diagrams  show  how 
to  convert  well-known  circuits.   SOVEREIGN   ELECTRIC  & 
MANUFACTURING  COMPANY. 

41.  BABY  RADIO  TRANSMITTER  OF  9XH-9EK — Descrip- 
tion and  circuit  diagrams  of  dry-eel!  operated  transmitter. 
BURGESS  BATTERY  COMPANY. 

42.  ARCTIC  RADIO  EQUIPMENT — Description  and  circuit 
details   of  short-wave   receiver   and    transmitter   used   in 
Arctic  exploration.  BURGESS  BATTERY  COMPANY. 

58.  How  TO  SELECT  A  RECEIVER — A  commonsense 
booklet  describing  what  a  radio  set  is,  and  what  you  should 
expect  from  it.  in  language  that  any  one  can  understand. 
DAY-FAN  ELECTRIC  COMPANY. 

67.  WEATHER  FOR  RADIO — A  very  interesting  booklet 
on  the  relationship  between  weather  and  radio  reception, 
with  maps  and  data  on  forecasting  the  probable  results. 
TAYLOR  INSTRUMENT  COMPANIES. 

(Continued  on  page  55) 


RADIO  BROADCAST  ADVERTISER 


55 


73.  RADIO  SIMPLIFIED — A  non-technical  booklet  giving 
pertinent  data  on  various  radio  subjects.  Of  especial  in- 
terest to  the  beginner  and  set  owner.  CROSLEY  RADIO  COR- 
PORATION. 

76.  RADIO  INSTRUMENTS — A  description  of  various 
meters  used  in  radio  and  electrical  circuits  together  with  a 
short  discussion  of  their  uses.  JEWELL  ELECTRICAL  IN- 
STRUMENT COMPANY. 

78.  ELECTRICAL  TROUBLES — A  pamphlet  describing 
the  use  of  electrical  testing  instruments  in  automotive  work 
combined  with  a  description  of  the  cadmium  test  for  stor- 
age batteries.  Of  interest  to  the  owner  of  storage  batteries. 
BL-RTON  ROGERS  COMPANY. 

95.  RESISTANCE  DATA — Successive  bulletins  regarding 
the  use  of  resistors  in  various  parts  of  the  radio  circuit. 
INTERNATIONAL  RESISTANCE  COMPANY. 

96.  VACUUM  TUBE  TESTING — A  booklet  giving  pertinent 
data  on  how  to  test  vacuum  tubes  with  special  reference  to 
a    tube   testing   unit.    JEWELL    ELECTRICAL    INSTRUMENT 
COMPANY. 

98.  COPPER  SHIELDING — A  booklet  giving  information 
on  the  use  of  shielding  in  radio  receivers,  with  notes  and 
diagrams  showing  how  it  may  be  applied  practically.  Of 
special  interest  to  the  home  constructor.  THE  COPPER  AND 
BRASS  RESEARCH  ASSOCIATION. 

99.  RADIO   CONVENIENCE    OUTLETS — A    folder   giving 
diagrams  and  specifications  for  installing  loud  speakers  in 
various  locations  at  some  distance  from  the  receiving  set. 
YAXLEY  MANUFACTURING  COMPANY. 

105.  COILS — Excellent  data  on  a  radio- frequency  coil 
with  constructional  information  on  six  broadcast  receivers, 
two  short-wave  receivers,  and  several  transmitting  circuits. 
AERO  PRODUCTS  COMPANY. 

106.  AUDIO    TRANSFORMER — Data    on    a   high-quality 
audio  transformer  with  circuits  for  use.  Also  useful  data  on 
detector  and  amplifier  tubes.  SANGAMO  ELECTRIC  COMPANY. 

107.  VACUUM    TUBES — Data  on    vacuum   tubes  with 
facts  about  each.  KEN-RAD  COMPANY. 

108.  VACUUM  TUBES — Operating  characteristics  of  an 
a.c.  tube  with  curves  and  circuit  diagram  for  connection 
in  converting  various  receivers  to  a.c.  operation  with  a 
four-prong  a.c.  tube.  ARCTURUS  RADIO  COMPANY.. 

109.  RECEIVER  CONSTRUCTION— Constructional  data  on 
a   six-tube  receiver   using    restricted    field  coils.      BODINE 
ELECTRIC  COMPANY. 

i  io.  RECEIVER  CONSTRUCTION — Circuit  diagram  and 
constructional  information  for  building  a  five-tube  set 
using  restricted  field  coils.  BODINE  ELECTRIC  COMPANY. 

in.  STORAGE  BATTERY  CARE— Booklet  describing  the 
care  and  operation  of  the  storage  battery  in  the  home. 
MARKO  STORAGE  BATTERY  COMPANY. 

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simplified  methods  of  including  various  power  tubes  in 
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"^'""A     \r\  I^p* 


RADIO  THEORY  AND  OPERATING.  By  Mary 
Texanna  Loomis.  Chapters,  44.  Pages,  886. 
Illustrations  632.  Loomis  Publishing  Company, 
Washington,  D.  C.  Price,  $3.50. 

RADIO  Theory  and  Operating"  is  one  of 
the  most  comprehensive  volumes  so  far 
published  in  its  field,  covering  not  only 
radio  theory  and  circuits  but  also  the  necessary 
electrical  engineering  required  in  the  operation 
of  radio  telegraph  and  radio  telephone  trans- 
mitters and  receivers. 

The  book  is  obviously  a  product  of  most  ex- 
tensive and  painstaking  research  and  reading, 
and  familiarity  with  the  work  of  the  best  au- 
thorities on  radio  subjects.  <It  is  now  issued,  re- 
cently revised,  in  its  third  edition. 

There  are  two  possible  treatments  of  compre- 
hensive works  on  radio  subjects.  A  book  may  be 
designed  to  appeal  to  the  radio  enthusiast  who 
desires  to  understand  thoroughly  the  theory  and 
operation  of  radio.  It  may  also  be  planned  for  the 
professional  radio  man  who  studies  the  subject 
as  a  member  of  a  class  conducted  by  an  expert 
teacher.  Miss  Loomis's  book  is  decidedly  in  the 
latter  classification.  Her  treatment  of  the  subject 
is  in  a  matter  of  fact  and  unromantic  style.  This 
is  not  written  in  the  spirit  of  condemnation,  but 
merely  to  define  the  author's  point  of  view. 

The  work  is  divided  into  four  parts.  The  first, 
of  twenty-five  chapters,  discusses  the  principles 
of  transmitting.  There  are  seventeen  chapters 
dealing  with  the  principles  of  electricity  and 
magnetism,  generators,  condensers,  transform- 
ers, and  the  essential  parts  of  the  radio  trans- 
mitter before  we  come  to  Chapter  XVI II, 
dealing  with  oscillating  currents.  Thus  the 
groundwork  is  thoroughly  laid  before  radio  cir- 
cuit principles  are  considered.  The  second  part 
deals  with  receiving  circuits,  in  eleven  chapters; 
the  third,  devoted  to  vacuum  tubes  and  con- 
tinuous waves,  comprises  six  chapters;  the 
fourth,  entitled  "The  Practical  Radio  Operator," 
covers  that  subject  with  eight  chapters. 

To  substantiate  my  point  that  the  book  is 
based  more  on  reading  and  research  than  upon 
practical  experience  in  the  handling  of  radio 
equipment  (not  that  the  author  is  without  ex- 
tensive practical  experience),  this  last  section 
quotes  liberally  and  thoroughly  digests  the  Gov- 
ernment regulations  applying  to  radio,  abbre- 
viations used  in  practice,  message  forms,  traffic 
regulations,  and  the  forms  used  in  practical  ship- 
to-shore  operating,  all  material  obtainable  by 
research  and  consultation  of  authorities.  On  the 
other  hand,  when  the  author  deals  with  troubles 
which  may  be  encountered  in  the  operation  of 
transmitters  and  receivers,  that  clearness  and 
completeness  which  otherwise  characterizes  the 
book  is  somewhat  lacking.  For  example,  the 
operation  of  crystal  control  in  broadcasting  sta- 
tions is  disposed  of  in  the  following  paragraph: 

"When  crystal  control  is  used,  too  high  a  volt- 
age must  not  be  placed  on  the  crystal,  as  this 
may  break  it.  From  300  to  400  volts  appears  to 
be  the  limit  that  the  crystal  can  stand.  Crystals 
are  a  great  help  in  keeping  the  oscillation  fre- 
quency constant  and,  by  eliminating  wastes  due 
to  wild  oscillations,  the  radiation  is  increased. 
However,  the  crystals  are  not  imperishable. 
They  need  care  and  have  to  be  replaced  occa- 
sionally." 

The  same  characteristic  of  treatment  may  be 
observed  in  the  discussion  of  possible  troubles 
with  receiving  sets: 

"If  upon  sitting  down  to  listen,  on  what  ap- 
pears to  be  a  correctly  wired  receiving  set, 
nothing  is  heard,  aside  from  the  possibility  of 
an  error  in  the  circuit,  this  may  be  caused  by 
something  very  simple.  The  trick  is  to  find  the 


simple  cause.  Perhaps  the  most  common  cause 
of  this  is  a  short-circuited  fixed  condenser,  either 
shunted  across  the  telephone  circuit  or  the  first 
amplifying  transformer.  This  may  be  caused 
by  the  use  of  a  hot  soldering  iron  as  a  con- 
denser composed  of  copper  or  tin  foil  and  waxed 
paper,  is  not  intended  to  withstand  heat.  Where 
fixed  condensers  are  soldered  into  a  circuit, 
this  must  be  done  very  cautiously.  Probably  the 
next  most  important  cause  for  silence  in  a  re- 
ceiving set  is  a  poor  contact  between  the  prongs 
on  the  base  of  the  tubes  and  the  springs  in  the 
socket.  Springs  should  press  tightly  against  the 
prongs,"  etc.,  etc., 

Considering  that  the  volume  is  entitled 
"Radio  Theory  and  Operating"  and  not  merely 
"  Radio  Theory,"  possibly  a  better  balanced 
book  would  have  been  produced  by  more  com- 
plete and  systematic  arrangement  of  possible 
troubles  encountered  in  the  operation  of  trans- 
mitting and  receiving  apparatus. 

Another  peculiarity  of  the  book  is  the  meticu- 
lous care  observed  in  giving  credit  to  independent 
inventors  whose  work  antedated  those  generally 
given  credit  for  radio's  important  inventions. 
Unquestionably  this  attitude  arises  out  of  the 
fact  that  Miss  Loomis's  father  is  Dr.  Mahlon 
Loomis,  who  demonstrated  radio  transmission 
and  reception  in  1872,  in  Virginia.  His  pioneer 
work  is  not  generally  recognized.  A  patent  was 
issued  him  on  July  30,  1872,  and  his  demonstra- 
tions, a  matter  of  public  record,  establish  his 
priority  over  Marconi.  But  history  invariably 
credits  the  man  who  first  puts  over  a  new  idea 
or  system  commercially,  whether  he  is  the  first 
inventor  or  not. 

Doctor  Loomis  bears  the  same  position  in 
radio  that  Dr.  Samuel  Langley  holds  in  aero- 
nautics. The  Wright  brothers  are  credited  with 
the  invention  of  the  airplane  because  they  were 
the  first  to  demonstrate  it  to  the  general  public 
so  that,  through  their  influence,  it  has  won  recog- 
nition as  a  practical  device.  Glenn  H.  Curtis, 
substituting  a  modern  motor  for  the  steam 
engine  originally  installed  as  motive  power  in 
1897,  made  Langley 's  plane  fly  successfully. 
But  even  this  vindication  of  Langley  has  not 
deprived  the  Wright  brothers  of  their  position 
as  the  acknowledged  inventors  of  the  airplane. 

Miss  Loomis's  book  is  to  be  recommended 
particularly  to  commercial  wireless  telegraph 
operators.  The  chapters  dealing  with  the  care 
of  storage  batteries,  the  functioning  and  care  of 
motor  generators  and  power  equipment,  and  the 
regulations  applying  to  commercial  practice 
are  thorough  and  complete.  An  extensive  series 
of  questions  at  the  back  of  the  book  are  helpful 
in  preparing  for  Government  examinations. 
Standard  ship  and  commercial  installations  are 
quite  thoroughly  dealt  with.  The  volume  is  well 
indexed  and  well  arranged. 

— EDGAR  H.  FELIX. 

Another  Text  for  Operators 

PRACTICAL  RADIO  TELEGRAPHY,  by  Arthur  R. 
Nilson  and  J.  L.  Hornung,  McGraw-Hill  Book 
Co.,  Inc.,  380  pages,  $3.00. 

TH  E  preface  to  this  book  states  that  it  is  writ- 
ten for  radio  students  preparing  to  become 
radio  operators.  Its  scope  is  therefore  marine 
radio  telegraphy,  and  does  not  include  broad- 
casting. At  first  it  may  seem  that  enough  books 
have  been  written  to  aid  aspiring  young  electri- 
cians to  survive  the  terrors  of  the  government 
license  examination,  but  this  book  really  does 
the  job  extraordinarily  well;  better,  I  believe, 
than  any  previous  work  on  the  subject.  The  art 
has  changed,  and  most  of  the  earlier  treatments 


RADIO  BROADCAST  ADVERTISER 


BOOK  REVIEWS 

(Continued  from  page  56) 

Practical  Radio  Telegraphy — Nilson  and  Hornung 

are  out  of  date.  This  fact,  as  well  as  the  long 
experience  of  the  authors  in  the  training  of  radio 
operators,  justifies  the  appearance  of  the  present 
volume. 

The  treatment  begins  with  the  physical  funda- 
mentals of  the  art,  the  first  seven  chapters  being 
devoted  to  such  topics  as  magnetism,  motors 
and  armatures,  and  characteristics  of  alternat- 
ing current  circuits.  The  treatment  is  nowhere 
skimpy;  in  the  chapter  on  armatures,  for  ex- 
ample, the  elements  of  armature  winding  are 
fully  described.  Wherever  physical  principles 
are  expressed  the  atomic  theory  is  used.  Occa- 
sionally the  phraseology  is  a  little  dubious,  as 
in  the  discussion  of  dielectric  breakdown  on 
page  107,  where  the  authors  tell  us  that  "a  rup- 
tured insulator  might  be  defined  as  a  material 
in  which  the  electrons  have  been  extended  be- 
yond their  limit,  or,  in  other  words,  the  elec- 
trons have  been  strained  beyond  the  elastic 
limit  of  the  atomic  structure.  ..."  A  strained 
electron  might  tax  the  conceptual  powers  of 
greater  intellects  than  those  of  average  young 
men  studying  to  become  brass  pounders  on  the 
high  seas.  But  the  explanations  are  in  the  main 
clear  and  scientific;  the  one  which  has  been 
quoted  is  not  a  fair  example. 

Photographs  and  practical  illustrations  of  ap- 
paratus have  been  secured  from  manufacturers 
and  communication  companies.  Spark,  vacuum 
tube,  and  arc  transmitters  for  marine  use,  com- 
mercial receivers,  and  the  radio  compass,  .are 
thoroughly  described.  Questions  at  the  end  of 
each  chapter  may  be  used  by  the  student  to  test 
his  knowledge.  Most  of  the  chapters  are  written 
to  the  length  of  a  normal  assignment  in  a  radio 
school.  The  printing  is  first-rate,  with  the  ex- 
ception of  a  comical  error  in  the  running  head 
of  Chapter  XXI.  The  book  includes  an  index. 
It  is  written  for  readers  who  lack  preparation 
in  elementary  electricity,  mathematics,  and 
chemistry,  gives  them  what  they  need  of  such 
prerequisites,  carries  them  through  the  tech- 
nique of  radio  marine  telegraphy,  and  fills  the 
need  for  a  reference  book  for  finished  operators. 
— CARL  DKI-HI-K. 


In  sending  the  coupon  below,  make  sure  that  your 
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written. 


USE  THIS  BOOKLET  COUPON 

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DIRECT  SELLING  BY  RADIO 

Is  It  a  Menace  to  the  Retail  Business  Structure? 


By  Francis  St.  Austell 

President,  Iowa  Radio  Listeners'  League 


LIT  in  Iowa,  the  haunt  of  direct  selling 
by  radio,  all  arguments  for  and  against 
"Direct  Advertising"  and  "Indirect 
Advertising"  have  been  abandoned  in  favor  of  a 
heated  controversy  on  the  subject  of  direct  selling 
by  radio.  Advertising,  direct  and  indirect,  has 
in  the  case  of  some  radio  stations,  given  place  to 
urgent,  persistent,  forceful  and  vociferous  clam- 
oring for  orders  for  all  kinds  of  commodities. 

The  three  terms,  indirect  advertising,  direct 
advertising  and  direct  selling  have  been  defined 
as  follows:  Indirect  advertising  is  the  type  of 
publicity  sent  out  by  a  great  number  of  stations 
including  those  on  the  networks.  It  consists  of 
the  name  of  the  advertiser  who  sponsors  the  en- 
tertainment, with  a  mention  of  products  in  a 
manner  calculated  to  create  good  will  and  also 
help  all  who  are  concerned  in  the  merchandising 
of  those  products.  Direct  advertising  consists  of 
the  broadcasting  of  requests  for  orders,  with  or 
without  price  quotations  sent  out  by  a  station 
which  has  sold  time  to  an  advertiser  for  the 
purpose  of  selling  goods  by  radio.  Direct  selling 
consists  of  the  solicitation  of  orders  by  a  station 
which  sells  goods  direct  to  the  consumer  for  its 
own  account  and  for  its  own  profit. 

The  center  of  the  controversy  is  quite  naturally 
Iowa,  because  the  principal  direct  selling  stations 
are  located  in  that  state.  The  writer  is  not  famil- 
iar with  the  situation  in  other  states,  but  is 
certainly  very  familiar  with  the  Iowa  station 
which  is  probably  unique  or  ought  to  be. 

A  half-hour  period  usually  called  the  "Letter 
Basket"  has  just  been  brought  to  a  close  by  the 
owner  and  operator  of  KFNF  Shenandoah.  This 
station  was  the  first  to  adopt  the  plan  of  selling 
directly  to  consumers  and  is  still  the  chief  expo- 
nent of  the  art.  During  the  period  referred  to,  the 
public  was  begged  to  send  orders  for  tires,  dishes, 
peaches.'coffee,  Chinese  baskets,  pencils,  fountain 
pens  (guaranteed  for  life)  suits,  overcoats,  paint, 
canned  corn  and  nursery  stock,  not  forgetting 
prunes.  Before  the  advent  of  radio,  the  owner  and 
operator  of  KFNF  was  in  the  seed  and  nursery 
business.  The  other  lines  have  apparently  been 
added  since  the  issue  of  a  license  to  broadcast. 

KFNF,  Shenandoah,  is  now  self-announced  as 
the  "merchandise  center  of  the  middle  west"- 
"the  pioneer  trading  station"  and  somewhat 
vaguely  as  "the  world's  largest."  In  a  few  short 
years  a  business  primarily  devoted  to  seeds  and 
nursery  stock,  with  an  annual  turnover  of  prob- 
ably about  three  hundred  or  four  hundred  thou- 
sand dollars,  has  grown  with  the  aid  of  radio 
into  a  business  with  a  volume  of  more  than 
three  million  dollars. 

The  entertainment  furnished  by  KFNF  is  not 
of  a  high  class  nature.  It  is  what  is  called  common 
music  for  common  people  or  simply  old-fashioned 
music  for  plain  folk.  While  the  response  from 
the  public  to  the  efforts  at  entertainment  is 
meager,  the  response  to  the  talks  broadcast  from 
that  station  is  enormous.  These  talks  are  really 
clever  and  deal  with  agriculture,  horticulture, 
household  hints  and  many  other  subjects. 
KFNF  has  a  following  which  numbers  many  hun- 
dreds of  thousands  and  every  one  of  them  will 
fight  if  his  favorite  station  is  criticized.  There 
is  probably  no  station  in  the  country  that  has 
such  a  loyal  following  and  some  extra  bitter 
opponents  of  direct  selling  say  that  no  other 
station  wants  such  a  following.  The  opponents 


of  direct  selling  are  divided  into  two  classes.  One 
class  wants  direct  selling  stations  to  be  put  off 
the  air  entirely.  The  other  would  be  content  if 
direct  selling  were  abolished  and  would  demand 
nothing  more. 

Henry  Field  of  KFNF,  just  plain  "Henry"  to 
his  friends,  has  a  magnetic  personality  which 
reaches  out  and  grips  his  audience.  His  descrip- 
tion of  a  cup  of  his  famous  coffee  is  tantalizing 
and  his  vivid  picturization  of  a  cooked  slice  of 
his  wonderful  ham  just  makes  one's  mouth  water. 
His  coats  are  the  best  ever  heard  of,  his  overalls 
are  works  of  art,  his  tires  make  motoring  a  joy 
forever,  his  canned  peaches  bring  to  our  table 
the  sunshine  of  California.  It  is  a  bad  day  when 
his  sales  talks  do  not  bring  a  few  thousands  of 
dollars  to  the  merchandise  center. 

THE    FINE    ART    OF    RADIO    SELLING 

HENRY  FIELD  has  developed  salesmanship 
by  radio  into  a  very  fine  art — so  fine  an  art 
in  fact  that  many  claim  that  if  his  example  were 
followed  by  others  fortunate  enough  to  own  a 
radio  station,  the  whole  retail  business  structure 
of  the  country  might  be  endangered.  The  selling 
of  merchandise  by  radio  is  so  profitable  that  it  is 
surprising  to  find  so  few  radio  stations  engaged  in 
the  pastime. 

Those  who  oppose  direct  selling  as  unfair 
competition  ask:  "  If  one  broadcaster  is  allowed 
to  use  the  greater  part  of  his  time  on  the  air  for 
the  purpose  of  soliciting  orders,  why  should  not 
every  broadcaster  do  it?  Why  should  not  every 
man  be  given  the  right  to  erect  and  operate  a 
radio  station,  provided  he  expresses  the  willing- 
ness or  desire  to  sell  prunes,  peaches,  tires,  over- 
alls and  other  commodities?" 

At  present,  the  local  dealer  who  has  no  broad- 
casting station  is  in  an  unfortunate  position.  He 
is  open  to  attack,  direct,  indirect,  by  accusation 
and  by  innuendo.  Not  having  a  radio  station  from 
which  to  shout,  he  is  naturally  at  a  loss  for  a 
reply.  He  gets  sore  and  thinks  of  all  kinds  of 
smart  "come  backs,"  but  he  has  to  remain  silent. 

It  is  not  unusual  to  hear  over  the  air  remarks 
to  the  effect  that  "your  local  merchant  would 
charge  you  at  least  twelve  dollars — but  by  buy- 
ing from  this  station,  you  get  it  for  seven  dollars." 
The  purchaser  by  radio  also  has  the  extra  and 
exquisite  pleasure  of  hearing  his  name  "read 
out."  The  price  comparison,  according  to  reports 
from  dealers,  is  not  always  fair  or  absolutely 
correct,  but  who  can  contradict  it? 

KFNF  sometimes  issues  statements  to  the  effect 
that  the  station  does  not  undersell  competitors 
and  claims  "quality"  as  the  keynote  of  its  busi- 
ness policy.  At  another  time,  the  station  claims 
to  have  forced  down  prices  on  many  commodities 
and  to  have  saved  the  farmer  vast  sums  of  money. 
Whether  or  not  they  save  money  or  get  better 
quality  the  loyal  followers  of  Henry  send  their 
cash  to  his  station  and  demand  that  he  be  allowed 
to  do  as  he  likes  with  his  radio  station. 

It  has  been  stated  that  the  direct  selling  sta- 
tions of  Iowa  can  produce  five  hundred  thousand 
signatures  to  support  their  claims  to  popularity. 
This  is  no  doubt  a  very  low  estimate.  But  it  may 
be  asked  whether  the  popularity  of  a  station  is 
sufficient  excuse  for  what  many  regard  as  the 
evils  of  direct  selling.  On  this  subject  a  correspon- 
dent remarks  "  popularity  has  nothing  to  do  with 


RADIO  BROADCAST  ADVERTISER 


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DIRECT    RADIO    SELLING 

by  Francis  St.  Austell 

(continued  from  page  58) 

it.  Saloons  were  popular  once,  but  where  are 
they  now?"  Correspondence  comes  from  all  over 
the  country,  from  Rhode  Island  to  California, 
from  Maine  to  New  Mexico,  and  it  is  a  very  note- 
worthy fact  that  most  letters  from  opponents  of 
the  principles  of  direct  selling  are  on  excellent 
paper  and  represent  a  highly  educated  class, 
while  those  from  supporters  of  the  direct  seller  are 
for  the  most  part,  extremely  hard  to  read,  are 
not  noted  for  cleanliness  and  usually  avoid  refer- 
ence to  the  real  subject  of  debate.  The  popularity 
of  KFNF  is  based  on  its  talks,  its  gospel  hymns, 
religious  services  and  its  old-fashioned  music. 
The  opponents  of  direct  selling  do  not  necessarily 
criticize  these  features,  but  the  loyal  followers  of 
KFNF  see  in  an  attack  on  direct  selBng.-a  camou- 
flaged attack  on  the  gospel.  They  want  Henry 
or  "Henery"  and  resent  any  suggestion  of  criti- 
cism, even  of  the  station  presided  over  by  their 
idol.  The  owner  and  operator  of  KFNF  recently 
broadcast  a  statement  to  the  effect  that  those 
who  did  not  like  his  station  were  writing  to  the 
Federal  Radio  Commission,  telling  that  body 
all  about  it.  He  also  commented  on  the  fact  that 
these  people  were  sending  typewritten  letters. 
The  young  lady  who  sorts  my  mail  was  discov- 
ered once  making  two  piles  of  letters  before  open- 
ing them.  One  was  a  clean,  neat  pile,  the  other 
was  quite  different.  When  asked  the  reason  for 
such  a  procedure,  she  remarked  "The  clean  ones 
object  to  direct  selling,  the  dirty  letters  support 
it."  Quite  simple,  but  also  very  significant.  Of 
course  their  are  some  very  clean  and  well  written 
letters  favoring  direct  selling  but  these  are  con- 
spicuous in  comparison. 

WHERE  DIRECT  SELblNG  IS  POPULAR 

AT  A  convention  in  Des  Moines,  held  last 
year,  a  speaker  attacked  the  principles  of 
direct  selling,  without  mentioning  any  stations 
by  name.  Mr.  Field  of  KFNF  requested  that  bar- 
riers be  let  down  and  that  the  matter  be  dis- 
cussed openly,  as  he  said  he  was  quite  aware  the 
remarks  referred  to  him.  The  way  followers  of 
Shenandoah  rallied  to  his  support  was  an  eye 
opener  to  many.  Women,  who  would  ordinarily 
dread  the  ordeal  of  a  public  appearance,  spoke 
fearlessly  and  eloquently,  facing  with  real  de- 
termination a  crowded  convention  hall.  Farmers 
and  their  wives  told  of  what  Henry  had  done  for 
them,  and  they  left  not  the  slightest  doubt  as  to 
the  popularity  of  Henry  Field  among  his  im- 
mediate followers.  To  his  opponents,  he  repre- 
sents probably  the  most  unpopular  station  in  the 
world.  Popularity  is  not  the  right  word.  This 
man,  Henry  Field,  arouses  a  feeling  among  his 
followers  that  is  akin  to  worship.  He  is  becoming 
a  cult.  The  reasonable  opponents  of  direct  selling 
do  not  hesitate  to  give  him  credit  for  all  the  good 
things  he  has  done.  They  fight  with  him  on  the 
points  only  of  direct  selling  and  the  methods  em- 
ployed in  merchandising. 

All  the  foregoing  remarks  can  be  applied  to 
other  stations,  of  course,  as  far  as  merchandising 
is  concerned;  but  the  magnetic  personality  of 
Henry  Field  makes  him  stand  alone,  a  national 
figure,  a  creation  of  radio,  a  leader  of  hundreds 
of  thousands,  almost  a  prophet,  a  Moses  of  the 
common  people. 

It  would  seem  that  the  direct  selling  stations 
sometimes  act  as  agents  for  manufacturers  and 
merchants,  while  certain  commodities  are  bought 
outright  and  sold  by  the  station  which  is  in  real- 
ity a  mail  order  house,  with  a  catalog  and  also 
the  additional  advantage  of  having  a  radio 
station  from  which  to  broadcast  bargains.  All 


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on  what's  up  to  date. 

Standard  Discounts  to  Dealers,  Set 
Builders,    Agent*. 

It  will  pay  you  to  get  our  prices  for  com- 
plete parts  for  the  popular  circuits  featured  In 
radio  magazines.  Whenever  a  now  circuit  appears 
for  which  you  want  complete  parts,  write  or  wire 
us  and  they'll  be  on  their  way  to  you  iiuk-kly. 
\Ve  know  what  parts  to  send  you.  Simply  give 
name  of  circuit  and  we'll  take  care  of  the  rest 
We  guarantee  you  a  big 
saving  on  every  order. 

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catalog  to-day  before  you 
spend  another  cent.  Mail 
the  coupon  and  free  copy 
will  be  sent  you. 


l)ept.  835 
Chicago,  i  .  8.  A. 
Mall  This  Coupon  Now!    For  Free  Copy 

Name    

Address    


DIRECT    RADIO    SELLING 

by  Francis  St.  Austell 

(continued  from  page  5p) 

goods  are  sold  with  a  money  back  guarantee. 
Even  the  hams  can  be  cooked,  partly  consumed 
and  the  remainder  sent  back  if  not  satisfactory. 

As  an  indication  of  the  volume  of  business  done 
figures  recently  broadcast  from  one  of  the  so- 
called  "farm  stations"  are  given  here.  They  in- 
dicate sales  since  February,  1927. 

55  carloads  of  tires — 400,000  pounds  of  coffee 
— 100,000  overalls  and  jackets,  30,000  work  and 
dress  shirts,  70,000  dress  patterns  of  j-J-  yards 
each — 10,000  ready  made  dresses — 24  carloads 
of  prunes — 60,000  pairs  of  silk  stockings — 50,000 
radio  tubes — 3000  suits  and  overcoats  since 
October  1927;  that  represents  only  a  part  of  the 
business  of  one  radio  station.  To  the  writer,  the 
figures  do  not  appear  in  any  way  exaggerated. 

Retail  merchants  are  becoming  alarmed,  fol- 
lowers of  the  farm  stations  are  elated.  The  so- 
called  farm  stations  claim  the  support  of  farmers 
as  a  class.  One  farmer  writes  and  states  plainly 
that  it  is  a  damned  lie  to  say  that  all  farmers  are 
in  favor  of  direct  selling.  Another  is  equally  posi- 
tive that  farmers  are  all  for  it. 

That  broadcasters  themselves  are  not  entirely 
united  on  the  subject  of  direct  selling  is  indicated 
by  the  following  quotation  from  a  letter  ad- 
dressed to  the  writer  by  the  secretary  of  the 
Berry  Seed  Company,  which  owns  and  operates 
station  KSO,  Clarinda,  Iowa,  This  station  was  en- 
gaged in  the  direct  radio  sale  of  seeds  and 
kindred  lines.  The  letter  says,  in  part: 

"The  question  of  direct  selling  or  the 
quotation  of  prices  over  the  radio  is  one  that 
is  receiving  much  discussion  not  only  in  Iowa 
but  in  many  other  sections  of  the  United 
States.  .  .  .We  cannot  help  but  come  to 
the  conclusion,  after  considering  the  matter 
from  all  angles,  that  it  does  give  such  firms 
an  undue  advantage  over  competitors  who 
have  no  radio  station  or  access  to  one  over 
which  their  prices  may  be  quoted.  This 
might  readily  be  termed  an  unfair  advantage 
and  perhaps  for  that  reason  alone  should  be 
eliminated.  .  .  .  To  return  to  our  former 
statement,  we  would  welcome  an  order  to 
desist  from  quoting  prices.  We  welcome  a 
mutual  agreement  that  would  eliminate  it, 
and  if  neither  of  these  occur,  we  shall  perhaps 
cease  anyhow." 

An  ardent  supporter  of  direct  selling  principles 
was  asked  by  the  writer  if  he  could  produce  one 
logical  argument  in  favor  of  it,  merely  said:  "The 
broadcaster  was  lucky  and  he  found  a  gold  mine 
in  a  radio  station.  There  is  no  law  against  using 
a  gold  mine." 

There  is  no  law  to  prevent  a  man  from  being 
lucky  enough  to  find  and  use  a  gold  mine,  but 
unfortunately,  there  is  a  law  which  prevents  a 
lot  of  people  from  founding  a  broadcasting  sta- 
tion. One  station  of  the  direct  selling  kind,  accord- 
ing to  its  own  report,  annually  sends  out  cata- 
logues to  the  number  of  a  million  and  a  half. 
The  follow-up  to  these  catalogues  consists  of 
direct  selling  talks  by  radio.  Catalogues  from 
other  firms  must  be  followed  up  by  mail.  It  looks 
a  bit  one-sided,  doesn't  it? 

The  Radio  Commission  announces  that  it  has 
not  been  given  the  power  to  dictate  to  a  broad- 
caster whether  or  not  he  should  sell  and  puts  the 
matter  up  to  the  public. 

Let  the  public  decide — as  quickly  as  possible. 


IAET 


NEW 
Adapter  Harness 

Makes  possible  the  usins  of  now 
A.  C.  tubes  in  present  set  with- 
out any  structural  alteration. 
Chanpe  ean  be  made  in  ten  min- 
utes. Eliminates  "A"  batteries. 
Use  your  present  "B"  and  "C" 
supply.  Complete  with  auxiliary 
volume  control.  $7.50  to  $9.50 
according  to  number  of  tubes. 

Write  for  illustrated 
folder 


\CYNCH/ 


Resistors  are  accurate,  per- 
manent, noiseless. 

1RTHUR  H.  LTNCH.  Inc..  1775  Bco.wdw.r,  N    r.  C. 


How  Does  Your  Receiver 
Work? 

What  Antenna  is  Best? 

How  Radio  Tubes  Func' 
tion? 

These  questions  and  many  others 
are  answered  in  Walter  Van  B. 
Roberts'  book,  "How  Radio  Re- 
ceivers Work." 

Today — send  one  dollar,  for  your 
copy,  to  the  Radio  Broadcast  Book- 
let Dept.,  Garden  City,  N.  Y. 


1928  Edition,  com- 
plete,   up-to-date. 
Full  information 
on  A.  C.  and  Screen 
Grid  Tubes.   Over 
90O  pages,  1025  illiu- 
trationi.  For  Service 
and   Repair    Men, 
Dealer*,   Salesmen, 
Experimenter*  and 
Designer!.  At  dealer* 
or  by  mail,  $6.00. 


FREDERICK  J.DRAKE  fc-CO. 

Michigan  Ave.         Chii 


RADIO  BROADCAST  ADVERTISER 


61 


5 -Prong  S-M 
Plug -In  Coils 

Economy — Efficiency 


For  the  popular  "tube  base"  short  wave  receiver  Silver-Marshall  will  have 
ready  on  June  1st,  new  types  of  moulded  Bakelite  coil  forms  and  wound  coils 
designed  to  fit  any  standard  5-prong  tube  socket,  such  as  S-M  512.  These  forms 
have  ample  winding  space  for  all  short  wave  or  broadcast  band  coils,  and  a 
tickler  slot  at  the  base.  Their  small  size  particularly  adapts  them  to  short  wave 
sets  to  provide  the  smooth  regeneration  necessary  to  telephone  or  rebroadcast 
reception  and  their  cost  Is  as  low  as  their  efficiency  and  flexibility  is  high. 
Type  130  blank  forms  can  be  had  with  smooth  winding  space  I'/i"  In  diameter 

and  1^"  long,  with  tirkler  slot  and  pins  at   .50  each,  or  wtth  threaded  winding  space    (98  threads)    If  preferred.    A   variety 

of  typel  wound  for  different  purposes  can  be  had  at  $1.25  each  list.  Type  512  socket  which  fits  these  coils  is  priced  at  75c 
Why  pay  $8  00  to  *!''  01)  for  a  set  of  short  wave  colls  when  four  130  forms  and  a  512  socket  costing  $2.75  altogether 

plus  less  than  a  pound  of' wire  and  an  hour's  fun  will  give  you  as  pretty  a  little   set  of  coils,   tuning   from    17   to  over   200 

meters,  as  you'd  evec  want  to  see. 


The  Famous  S-M  240  Audio  Transformer 


WTO      I1J*1M      afOi      leaui-i      in      INI-     .iuun>     utivt     u*      imv      unvii  „     ,v»_i      —  •-••      —r-      -  -  —  ~ 

quality  in  any  set  you  buy  or  build.  Price,  240  audio,  3:1  ratio,   $b.OO;   241  output, 

ABC  and  B  Power  Units  to  Fit  in  Your  Set  Cabinet 


ready  to  assemble   $92.75. 


SILVER-MARSHALL,  Inc. 


SILVER-MARSHALL.  Inc.,  838  West  Jackson  Blvd.,  Chicago,  III 


I    enclose    :0c    for    which    please    send    me    full    Information   on   the    S-M 
audio  transformers,   power   supply  units,    unlpacs,    and  the   h-M   receivers. 
..I  enclose  25c  for  instructions  for  building  the   S-M  unlpacs. 
....      enclose   25c   for  Instructions   and    blueprints   (or  building   the    Shielded 

....I    enclose    2  5c    for    instructions    and    blueprints    for    building    the    S-M 
wave  tuners. 


The    new    S-M    "670"    Reservoir   Power    Units    are    but    13"    long. 

3%"  wide  and  « V4 "   high  over  the  280   rectifier  tube  they  use.   Both 

are    housed    in    attractive    brown   crystaline    steel    cases,    and   have    the 

features    that    made    the   older    652    and    656    Reservoir   B's   the   most 

popular  kits  of  their  type.  The  Clough  selective  flitter  and  a  new  volt- 
age divider  system  provide  unusually  <iuielness  and  freedom  from  motor- 
boating  on  any  set  of  one  to  ten  tubes.  670B  supplies  filed  voltages  of 
"""A  90  135  and  180  to  200  volts,  with  a  variable  tap  giving  from  22  V4 
to  90  volts.  6  70 ABC  supplies  the  same  B  power  and  A  and  C  power  to  any 

AC  tub!  Sl'i '  5  volts'  2  25  and  5-°  volts  A  for  up  to  seven  tu 

iMOMHrr  C  bias  for  the  tubes  used  obtained  by  suitable  resistors  In  the  set 
K70B  is  priced  at  $35.50  wired,  ready  to  use,  or  $33.00  in  kit  form,  with 
cabinet  ready  to  assemble.  670ABC  is  priced  at  $38.50  wired,  or  $3a.OO 
for  the  complete  kit  with  all  instructions. 

New  Unipacs  for  250  Tubes 

Two  Unipacs  taking  full  advantage  of  the  new  250  type  tube  are  ready,  one 
a  single  stage  Unlit  socket  power  amplifier  and  B  supply,  and  the  necnd  a 
wo  stage  amplifier  for  radio  or  phonograph.  Each  uses  one  UX-250  amplifier 
tube  to  furnish  4«T)0  milliwatts  of  undistorted  power  output,  which  means  just 
about  the  sweetest  fullest  tone  you've  ever  heard — just  a  shade  belter  than 


838  West  Jackson  Blvd.,  Chicago,  Illinois 


R.uno    BHOADCAST.      June. 


Published    monthly.      Vol.    XIII.    No.    2.      Published    at    Garden    City.    N.    Y.      Subscription    price    $-1.00    a   year.      Kntered    at    the    post    office    at 
Garden  City.   N".   Y..   as  second  class  mail  matter.      Doubleday,   Doran  &  Company.   Inc..   Carden   City.   N.    Y. 


RADIO  BROADCAST 


JUNE,  1928 


WILLIS  KINGSLEY  WING,  Editor 

KEITH  HENNEY  EDGAR  H.  FELIX 

Director  of  the  Laboratory  Contributing  Editor 


Vol.  XIII.  No.  2 


Cover  Design  -     -  From  a  Design  by  Harvey  Hopkins  Dunn 

Frontispiece  In  the  Grand  Canyon  of  the  Colorado 

How  Chain  Broadcasting  Is  Accomplished  -     -     -     -  C.  E.  Dean 
The  March  of  Radio      -  An  Editorial  Interpretation 


Broadcasting  Needs  Capable  Leadership 
Mergers  in  the  Radio  Industry 
More  High  Power  Broadcasting 


British  Skeptical  of  Baird  Television  Accorri' 

plishments 

Present  Distribution  of  Broadcast  Stations 
Here  and  There 


Automatic  Tuning  for  the  Radio  Receiver  - 

The  Newest  Power  Tube 

Book  Reviews 


Leroy  S.  Hubbell 

Howard  E.  Rhodes 

Carl  Dreher 


Lefax  Radio  Handbook 

Radio  Engineering  Principles,  Lauer  and  Brown 


A  Popular  Guide  to  Radio,  Dashiell 


The  "Cornet"  Multiwave  Receiver  -     -     -     -    W.  H.  Wenstrom 
From  Milliammeter  to  Multi'Meter -     -     -     -     -  G.  F. 
"Strays"  from  the  Laboratory 


Output  Transformer  Characteristics 
High  Powered  Press  Releases 
A.C.  Troubles 
May  Standard  Frequency  Signals 


Short-Wave  Notes 

Recent  Interesting  Contemporary  Articles 

Another  Useful  Publication 

Radio  School  Scholarships 


New  Apparatus  -     -  Useful  Information  on  J\[ew  Products 

A  Screen-Grid  Booster  for  Any  Receiver    -      Glenn  H.  Browning 
Our  Readers  Suggest 


An  Emergency  Detector  B  Supply 
Emergency  and  Experimental  Connections 
Volume  Control  for  Resistance-Coupled  Am- 
plifiers 


Some  Baffle-Board  Experiments 

Antenna  Tuning  Device 

A  Spark  Plug  Lightning  Arrester 


"Radio    Broadcast's"    Service    Data    Sheets    on    Manufactured 
Receivers    '*''*' 

No.  i.     The  Amrad  A.C.  7  No.  i.     The  Pfansteihl  A.C.  54  and  50. 

Building  and  Operating  the  A.  C.  "R.  B.  Lab"  Receiver 

Hugh  S.  Knowles 

Using  the  Screen-Grid  Tube  in  Popular  Circuits  Laboratory  Staff 
A  Good  Crystal  Receiver  for  the  Beginner  -  -  Keith  Henney 
A  Three-Tube  A.C.  Operated  Roberts  Receiver  Elmer  G.  Hery 
As  the  Broadcaster  Sees  It Carl  Dreher 


The  Simplest  Receiver 

Design  and  Operation  of  Broadcasting  Stations: 


ao.  Field  Strength  Measurements 


The  Listeners'  Point  of  Vieu> 

The  Month's  New  Phonograph  Records     -     -     * 
"Radio  Broadcast's"  Directory  of  Vacuum  Tubes 

Manufacturers'  Booklets 

"Radio  Broadcast's"  Laboratory  Information  Sheets 

No.  193.     Motorboating 

No.  194.     Push-pull  Amplifiers 

No.  195.     A    Resistitnce'Coupled    Amplifier 

with  Screen-Grid  Tubes 
No.  196.     Circuit   of  a   Resistance-Coupled 

Screen-Grid  Amplifier 

The  Haven  of  a  Sea'Going  Audion 


No.  197.     Amplification  Constant 

No.  198.     The  Screen-Grid  Tube  as  an  R.F. 

Amplifier 

No.  199.     Current 
No.  200.     Resistors 


64 
65 

68 


72 
74 
76  / 

77 
80 

83 


85 
87 

89 


93 
96 
97 
99 
1 02 


How  Can  Good  Radio  Programs  Be  Created?  -          John  Wallace     104 


106 
107 
108 
no 


Raymond  Travers     116 


I     AMONG  OTHER  THINGS. 


IT  HAS  not  been  possible  to  reply  with  a  personal  letter  to 
each  of  our  readers  who  filled  out  and  returned  the  readers' 
questionnaire  recently  sent  many  of  those  who  are  regular  sub- 
scribers. The  desires  and  opinions  of  readers  expressed  have 
been  very  helpful.  Many  interesting  conclusions  are  at  once 
apparent.  Our  policy  of  giving  complete  information  about  the 
manufactured  parts  described  in  constructional  articles  is  over- 
whelmingly approved.  The  type  and  form  of  the  articles  dealing 
with  the  construction  of  apparatus — such  articles  as  those  in 
this  issue  for  example — are  welcomed.  The  many  special  features 
and  articles  which  distinguish  RADIO  BROADCAST  from  its  con- 
temporaries are  especially  praised. 

SOME  readers  who  have  read  elaborate  statements  of  policy 
appearing  in  some  of  our  contemporaries  have  asked  us,  in 
effect,  if  we  were  going  to  announce  a  changed  policy,  too.  All 
we  have  to  say  about  the  editorial  policy  of  RADIO  BROADCAST 
has  been  said  in  this  column  in  the  May  issue.  This  magazine  is 
edited  for  the  reader  and  what  he  finds  in  RADIO  BROADCAST  is 
information — lots  of  it,  as  interestingly,  as  completely,  as  accu- 
rately presented  as  we  know  how.  This  magazine  will  neither  be 
full  of  inconsequential  and  slightly  sensational  articles  about  the 
marvelous  potentialities  of  radio  nor  will  it  overflow  with  con- 
structional articles  on  every  possible  subject  having  the  appar- 
ent purpose  of  merely  using  the  products  of  a  selected  group  of 
radio  manufacturers.  Our  policy  of  making  each  article  complete 
in  itself  and  not  "continued  on  page  06"  is  still  in  force.  The 
special  sections  which  have  so  wide  a  following:  the  Laboratory 
Data  Sheets,  the  March  of  Radio,  Strays  from  the  Laboratory, 
Our  Readers'  Suggest . .  . ,  As  the  Broadcaster  Sees  It,  the  Serv- 
ice Department,  are  to  be  continued.  With  this  issue,  we  intro- 
duce a  new  regular  feature:  "RADIO  BROADCAST'S  Service  Data 
Sheets  on  Manufactured  Receivers"  which  present  all  essential 
data  on  various  makes  of  sets  now  in  use.  Several  other  impor- 
tant new  features  are  in  the  course  of  preparation. 

EDGAR  H.  FELIX,  contributing  editor,  attended  the  pub- 
lic hearings  before  the  Radio  Commission  April  zj  and 
14.  He  appeared  as  an  expert  witness  and  presented  the  sugges- 
tions for  the  solution  of  the  broadcasting  problem  which  have 
attracted  such  wide  attention  in  our  editorial  section.  The 
March  of  Radio.  Incidentally,  we  are  told  that  Mr.  Felix's  May 
article  "Will  New  Transmitting  Methods  Be  the  Remedy''"  is 
accepted  in  Washington  as  the  most  clear  and  fair  presentation 
of  the  difficulties  and  possibilities  for  solution  of  the  present 
broadcast  situation. 

OUR  July  issue  promises  many  interesting  features.  There  is 
an  excellent  non-radiating  short-wave  receiver  using  a 
screen-grid  tube,  a  searching  analysis  of  the  almost  overwhelm- 
ing obstacles  to  practical  television,  the  description  of  a  fine  B 
supply  and  power  amplifier  using  the  250  type  tube,  a  practical 
set  tester,  and  many  other  articles,  selected  because  of  their 
unusual  interest. 

— WILLIS  KINGSLEY  WING. 


The  contents  of  this  magazine  is  indexed  in  The  Readers'  Guide 
to  Periodical  Literature,  which  is  on  file  at  all  public  libraries. 


OOUBLEDAT,  DORA^  &  ^OMPA^T,  D^C.,  Garden  Qity, 


MAGAZINES 


COUNTRY   LIKE 

WORLD'S  WORK 

GARDEN  &  HOME  BUILDER 

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WEST 

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OFFICERS 

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JOHN  J.  HESSIAN,  Treasurer 
LILLIAN  A.  COMSTOCK,  Assft  Secretary 
L.  J.  McNAUGHTON,  Asrft  Treasurer 


Copyright,  1928,  in  the  United  States,  Newfoundland,  Great  Britain,  Canada,  and  other  countries  by  Doubleday,  Doran  fi*  Company,  Inc.     All  rights  reserved. 

TERMS:  $4.00  a  year;  single  copie*  35  cents. 

62 


RADIO  BROADCAST  ADVERTISER 


Protect  yourA-C  tubes 

from  high  line  voltages 

'with 

t 

Ward  Leonard  Vitrohm 
Resistors  and  Rheostats 

Radio  receivers,  made  for  complete  operation  from  the 
power  lines,  are  designed,  usually,  to  operate  at  a  fixed 
line  voltage.  Where  the  line  voltage  exceeds  the  arbi- 
trary value  assumed  by  the  set  manufacturer,  damage  to 
the  tubes  may  result  unless  means  are  used  to  reduce 
the  line  voltage  to  the  value  at  which  the  set  is  designed 
to  operate. 

Two  methods  are  used,  ordinarily,  to  correct  for  exces- 
sive line  voltages;  a  resistor  or  rheostat  placed  in  series 
with  the  input  to  the  power  unit  of  the  receiver.  The 
resistance  value  and  current  carrying  capacity  of  these 
units  is  determined  by  the  receiver  primary  current  and 
the  maximum  potential  drop  required. 
Vitrohm  Resistors,  fitted  with  Edison  medium  screw 
bases,  are  the  most  convenient  units  to  use  where  fixed 
resistance  is  desired.  These  resistors  screw  into  a  series 
tap  which  is  in  turn  plugged  into  the  convenience  outlet 
or  socket.  They  are  priced  at  $2.00  each  and  are  avail- 
able in  the  resistances  listed  below: 


Catalog 
Number 

Resistance 
In  Ohms 

Catalog 
Number 

Resistance 
In  Ohms 

507-96 

2.5 

507-97 

15 

507-39 

3.5 

507-98 

22 

507-41 

5 

507-99 

31 

507-43 

7 

507-100 

45 

507-44 

10 

507-101 

62 

507-45 

12.5 

Vitrohm  4-inch,  11  step,  Rheostats  are  used  where 
adjustment  of  voltage  is  desirable  or  necessary.  Mount- 
ing may  be  either  front  or  back  of  panel.  The  price  is 
$5.50  each. 


Catalog 
Number 


Maximum  Resistance 
In  Ohms 


507-83 
507-59 
507-63 


12.5 
20 

50 


Your  dealer  stocks  Vitrohm  Resistors  and  Rheostats,  or  can 
get  them  (or  you.  Circular  512  describes  methods  of  line 
voltage  control  and  shows  complete  diagrams  of  circuit  con- 
nections. It  will  be  sent  to  you  promptly  upon  request 
without  charge. 

WARD  LEONARD  ELECTRIC  CO. 

MOUNT  VERNON,  N.Y. 
RESISTOR      SPECIALISTS      FOR      MORE      THAN      THIRTY-SIX       YEARS 


/n  //*e  Grand  Canyon  of  the  Colorado 


A  PORTABLE  radio  receiver  in  use  in  the 
Grand  Canyon  in  1923.  A  special  receiver  was 
built  for  the  expedition  by  the  Bureau  of  Standards 
which  was  carried  on  a  geological  survey  of  the 
Canyon  under  the  auspices  of  the  United  States 
Geological  Survey.  This  illustration  is  from  a  photo- 
graph by  Lewis  R.  Freeman,  of  the  Explorers'  Club, 
New  York,  who  was  a  member  of  the  expedition. 


Mr.  Freeman  explains  that  at  the  time  the  expedi- 
tion was  undertaken,  there  was  some  doubt  as  to 
whether  radio  reception  would  be  possible  in  the 
Canyon.  It  was  conclusively  demonstrated  that 
excellent  reception  was  possible.  The  receiver  per- 
formed as  well  at  depths  of  500  feet  as  at  5000,  Mr. 
Freeman  says.  The  antenna  in  the  illustration  also, 
it  seems,  served  the  party  as  a  clothesline. 


64 


CHAIN  broadcasting  is  known  to 
radio  listeners  as  a  means  whereby 
a  radio  program  may  be  transmitted 
by  several  or  even  dozens  of  radio  stations. 
Regular  networks  furnish  entertainment 
every  day,  and  on  important  occasions 
great  extensions  are  made  so  that  prac- 
tically the  entire  United  States  is  covered. 
The  estimated  audiences  at  such  times 
include  one  fourth  to  one  third  of  the 
entire  population  of  the  country.  More 
people  have  thus  listened  to  the  voice  of 
one  person  than  ever  before  in  history. 

The  apparatus  and  methods  whereby 
such  important  and  remarkable  results  are 
accomplished  are,  therefore,  interesting 
subjects  to  the  radio  fan.  His  knowledge  of 
vacuum  tubes,  audio-frequency  amplifiers, 
and  electrical  principles  will  enable  him 
to  appreciate  various  interesting  points  in 
the  equipment  and  operation  of  the  wire 
lines  used  in  chain  broadcasting. 

In  addition  to  the  long  lines  connecting  to 
radio  stations  in  distant  cities,  there  are 
many  shorter  lines  transmitting  programs, 
such  as  from  studios  centrally  located  in 
large  cities  to  the  powerful  radio  broad- 
casting apparatus  out  beyond  the  suburbs. 
Similar  circuits  are  used  to  broadcast 
sporting  events,  banquets,  and  other  occur- 
rences outside  the  studio,  thus  greatly  ex- 
tending the  range  of  program  features. 

It  is  one  of  the  duties  of  telephone  en- 
gineers and  operating  men  to  plan  and 
supervise  both  the  short  and  long  lines 
which  carry  radio  programs.  These  con- 
nections differ  in  various  respects  from 
regular  local  and  long  distance  telephone 
lines,  and  have,  therefore,  been  given  a 
special  name,  "program  circuits."  One 
difference  is  that  ordinary  telephone  circuits 
transmit  the  voice-  in  both  directions  (on  long 
circuits"  two-way  "amplifiers  are  therefore  neces- 
sary), but  in  program  circuits  it  is  necessary  to 
transmit  only  in  one  direction,  that  is,  from  the 
pick-up  microphone  to  the  one  or  more  radio 
transmitting  stations.  "One-way"  repeaters  are 
therefore  sufficient.  In  the  drawing  on  page  66 
arrows  indicate  the  diiection  of  transmission 
along  each  program  circuit  which  was  used  on 
January  4th,  1928,  the  date  of  the  first  Dodge 
Brothers  program.  The  regular  route  of  the  voice 
of  \\  ill  Rogers,  acting  as  master  of  ceremonies  at 
Los  Angeles,  may  be  followed  by  way  of  San 
Francisco  and  Denver  to  Chicago  and  the  East. 
\lso  an  additional  circuit  for  use  in  case  of  emer- 
gency is  seen  passing  through  southern  New 
Mexico,  Dallas,  and  St.  Louis  to  Chicago. 

MEETING     THE     TRANSMISSION     REQUIREMENTS 

ANOTHER  important  difference  between 
**  ordinary  telephone  circuits  and  program 
circuits  is  in  the  width  of  the  frequency  band 
transmitted.  In  a  telephone  conversation,  clear, 
intelligible  speech  is  desired,  and  it  has  been 
found  that  this  can  be  obtained  if  frequencies 
from  about  300  cycles  per  second  to  about  2000 
cycles  per  second  are  transmitted,  although 
modern  telephone  circuits  are  engineered  to  carry 
a  somewhat  wider  frequency  range.  However, 
with  program  circuits,  not  only  satisfactory  in- 
telligibility is  desired,  but  also  a  very  high  degree 
of  naturalness  and  faithfulness  in  the  transmis- 
sion of  music  and  speech  when  reproduced 
through  loud  speakers.  To  meet  these  require- 
ments, a  much  wider  band  of  frequencies  is  neces- 
sary. In  the  present  art  it  is  generally  considered 
desirable  to  transmit  a  range  of  frequencies  from 
about  100  cycles  per  second  to  about  5000  cycles 
per  second,  and  to  do  this  with  approximately 
uniform  efficiency.  In  this  way  the  low,  medium 


How  Chain  Broadcasting  Is  Accomplished 


By  C.  E.  Dean 

American  Telephone  and  Telegraph  Company 


THE  CHAIN  BROADCASTING  CONTROL  ROOM  IN  CHICAGO 

Similar  control  rooms  are  located  in  Boston,  Cincinnati,  Detroit,  St.  Louis,  Atlanta,  San  Francisco,  and  New 
York,  each  in  charge  of  a  "transmission  supervisor."  Repeaters,  oscillators,  equalizers,  transmission  measur- 
ing devices,  and  other  apparatus  necessary  in  the  exacting  work  of  transmitting  the  programs  are  shown  in 
the  illustration.  Cone  loud  speakers  are  mounted  in  the  protecting  frames  at  the  left.  During  operation,  one 
cone  is  connected  to  the  Red  network,  another  to  the  Blue,  a  third  to  the  Purple;  the  fourth  is  a  spare. 


and  high  pitch  ranges  of  music  and  other  program 
material  are  transmitted  with  a  considerable 
degree  of  faithfulness. 

In  addition  to  the  wider  frequency-range 
requirements,  program  circuits  are  called  upon 
to  transmit  greater  volume  variations  than  ordi- 
nary telephone  circuits.  For  example,  the  music 
of  a  symphony  orchestra  will  vary  from  a  very 
loud  intensity,  when  many  instruments  are 
sounding,  to  a  very  faint  intensity  at  other  times. 


What  Radio  Owes  to  Chain 
Broadcasting 

THE  Washington  air,  in  and  near  the 
halls  of  Congress,  has  been  full  of 
pointed  and  often  unpleasant  comments 
about  chain  broadcasting  during  the  recent 
weeks  when  the  last  radio  bill  was  under 
consideration.  Aside  from  the  political 
aspects  which  so  fascinate  our  legislators,  it 
can  be  said  without  fear  or  favor  that  chain 
broadcasting  is  responsible  almost  entirely 
for  the  growth  of  high-grade  programs  in 
this  country.  Chain  broadcasting  has  par- 
tially solved  the  old  question:  "Who  is  to 
pay  for  broadcasting?"  As  the  use  of  the 
wire  network,  linking  stations,  has  in- 
creased, so  has  the  radio  audience,  and 
with  it  the  time,  money,  and  effort  ex- 
pended on  programs.  This  article  explains 
some  of  the  technical  aspects  of  the  accomp- 
lishment, much  of  which  appears  for  the 
first  time. 

— THE  EDITOR. 


At  all  times  extraneous  noise  on  the  circuit  must 
be  slight  in  comparison  with  the  volume  of  the 
music.  The  critical  times  are  during  the  faint 
portions  of  the  program,  and  to  transmit  these 
satisfactorily,  a  very  quiet  circuit  is  obviously 
necessary. 

The  large  variations  in  the  volume  of  orches- 
tral music  (which  are  of  the  order  of  50  TU,  an 
energy  ratio  of  100,000)  are  greater  than  radio 
stations  can  transmit  without  overloading  on 
the  loud  signals  and  losing  the  faint  portions  in 
local  noise,  static,  etc.,  at  the  receiver.  So  at  the 
microphone  amplifier  one  of  the  broadcast 
station  control  operators  manipulates  the  ampli- 
fication control  so  as  to  reduce  these  variations, 
cutting  down  somewhat  the  loud  portions  and 
bringing  up  somewhat  the  faint  portions,  taking 
care  to  preserve  as  nearly  as  possible  the  natural- 
ness of  the  music.  The  program  circuits,  i.  e.,  wire 
lines  are  quiet  enough  to  be  able  to  more  than 
handle  all  the  volume  variation  which  the  broad- 
casting radio  stations  desire  to  transmit. 

Besides  the  requirements  just  considered,  the 
program  circuits  must  of  course  function  har- 
moniously with  the  other  circuits  of  the  telephone 
plant,  so  that  program  transmission  will  not  be 
overheard  on  the  ordinary  circuits,  nor  vice 
versa. 

For  short  connections  in  cities  and  at  other 
places,  circuits  in  cable  are  usually  employed. 
The  attenuation,  the  loss,  introduced  by  a 
seven-mile  length  of  iq-gauge  cable  pair  (con- 
sisting of  No.  10  B  &  S  copper  wire),  with  no 
loading  coils  or  other  apparatus  connected, 
increases  considerably  with  increase  of  fre- 
quency. One  TU  of  loss  means  a  reduction  of 
power  to  795  per  cent,  of  its  original  value,  two 
transmission  units  means  a  further  reduction  to 
79$  per  cent,  of  what  is  left,  or  to  .795  x  .705 
.63  =  63  per  cent,  of  the  original  amount. 


66 


RADIO  BROADCAST 


JUNE,  1928 


Three  TU  is  a  power  ratio  of  50  per  cent.,  four 
is  40  per  cent.,  and  five  TU  32  per  cent.  Twenty 
TU  is  a  power  reduction  to  o.oi  or  I  per  cent, 
of  its  original  value,  as  shown  by  the  bottom 
line  of  the  chart.  (TU  are  also  used  to  express  the 
amount  of  amplification,  or  "gain,"  of  an  am- 
plifier, the  ratio  being  the  reciprocal  of  that  for 
loss.  Thus,  20  TU  gain  is  .ojr  =  100  times,  mean- 
ing that  the  output  power  is  100  times  as  great 
as  the  input  power.  For  further  information  on 
TU  see  Martin,  Journal,  A.  I.  E.  E.  June,  1924). 

If  the  cable  mentioned  were  used  without 
any  correcting  agency  there  would  be  a  serious 
reduction  in  the  strength  of  the  high-pitch  com- 
ponents which  give  music  its  charm  and  bril- 
liancy. But  frequency  distortion,  if  not  too  great, 
can  be  offset  by  introducing  an  opposite  distor- 
tion, a  veritable  case  of  two  bad  elements  com- 
bined to  achieve  the  desired  good  result. 

To  correct  the  frequency  characteristic  of 
short  cable,  special  devices  called  "equalizers" 
are  used.  These  consist  of  inductance,  capaci- 
tance, and  resistanre,  three  of  the  elements 
forming  a  parallel  resonant  circuit,  such  as  is 
familiar  to  radio  amateurs  from  its  use  as  a 
wave-trap.  However,  here  the  elements  are  so 
chosen  that  the  resonant  frequency  is  far  lower, 
lying  a  little  above  the  range  of  frequencies 
which  the  circuit  transmits.  As  in  a  wave-trap, 
the  impedance  is  high  at  the  resonant  frequency, 
so  that  here  the  equalizer  introduces  little  loss 
since  it  is  shunted  across  the  line.  But  at  lower 
frequencies  the  impedance  is  much  less,  and  by 
proper  adjustment  of  the  two  resistances  and 
the  equalizer  is  made  to  have  characteristics 
just  the  opposite  of  those  of  the  cable  pair.  The 
resulting  curve  for  the  cable  with  the  equalizer 
is  practically  horizontal,  which  is  the  result  de- 
sired. The  volume  is  then  raised  to  a  higher 
level  by  a  distortionless  amplifier. 

For  the  long  connections  between  cities  in 
chain  broadcasting,  "open  wire"  circuits  are 
largely  used,  that  is,  circuits  consisting  of  wire 
on  insulators  supported  by  cross  arms.  Most  of 
this  wire  is  hard-drawn  copper  (No.  6  B.  &  S.) 
0.165  inches  in  diameter,  the  most  rugged  type 
of  open  wire  line  used  in  the  Bell  System.  The 
energy  loss  along  this  type  of  line  is  much  less 
than  along  an  equal  length  of  the  cable  just 
considered,  but  after  the  current  has  traveled 
about  two  or  three  hundred  miles  it  must  be  rein- 
forced. For  this  purpose  an  audio-frequency  am- 
plifier, called  a  "repeater,"  is  used. 


An  open  wire  circuit  is  similar  to  cable  in  that 
the  energy  loss  is  greater  at  high  frequencies, 
but  somewhat  different  methods  are  used  to 
make  the  open-wire  frequency  characteristic 
horizontal.  Repeaters  which  introduce  greater 
amplification  for  the  high  frequencies  are  used 
in  conjunction  with  equalizers.  These  equalizers 
are  different  from  the  cable  equalizer  since  the 
conditions  are  not  the  same. 

TELEGRAPH   AND  AMPLIFIER   ARRANGEMENTS 

PARALLELING  every  long  program  circuit 
is  a  telegraph  circuit  over  which  reports  and 
instructions  are  transmitted.  With  keys  and 
sounders  at  every  repeater  station  this  provides 
an  auxiliary  communication  channel  for  the  use 
of  those  responsible  for  the  program  circuit. 
Other  telegraph  circuits  connect  the  radio  sta- 
tions on  each  chain  with  the  key  station  for  the 
coordination  of  station  announcements  and  other 
program  details. 

One  of  the  most  interesting  features  of  a  pro- 
gram network  is  the  means  employed  to  restrict 
the  effect  of  an  accidental  short-circuit  of  the 
line  at  any  point.  Without  the  methods  used, 
such  a  short-circuit,  besides  preventing  any 
transmission  beyond  the  particular  point,  would 
greatly  reduce  the  voltage  for  a  considerable  dis- 
tance back  along  the  line.  Now  an  amplifier,  be- 
sides its  primary  purpose,  has  the  important 
property  that  a  change  in  the  condition  of  the 
output  circuit  (such  as  a  short),  has  practically 
no  effect  on  the  input  circuit.  So,  wherever  a 
program  circuit  forks,  an  amplifier  is  inserted 
into  each  outgoing  branch,  with  the  result  that 
a  short-circuit  across  one  branch  will  not  affect 
the  transmission  along  the  other  branch.  This  is 
done  regardless  of  whether  or  not  amplification 
is  needed — the  one-way  feature  of  an  amplifier 
is  taken  advantage  of  in  this  way  to  increase  the 
reliability  of  the  system.  For  this  reason  re- 
peaters average  about  125  miles  spacing  in  the 
East,  when  otherwise  two  or  three  hundred  miles 
would  be  sufficiently  close,  for  there  are  numerous 
forking  points  in  this  part  of  the  country. 

The  drawing  on  page  67  illustrates,  by  a  typi- 
cal case,  the  manner  in  which  the  power  decreases 
along  each  section  of  a  program  circuit  and  is 
built  up  to  its  original  value  at  the  repeater 
points.  For  example,  at  the  New  York  repeater 
station  the  incoming  power  from  the  radio 
studio  is  given  a  net  amplification  of  9  TU,  and 
then  begins  the  trip  to  Troy,  New  York. 


CHAIN  BROADCASTING  CIRCUITS  OPERATING 


ON  EVENING  OF  JANUARY  4.  1928. 

Otute  used  hx  Dcdgf  Brother  Program 


••""••-  Cimjrts  used  only  !w  otfwt  Program! 
Tolal  about  24.030  mite  ol  atari  or  44000  mi!« 
Conrwded  radio  station  «ere  wealed  *i  each  city  sho-n 


Along  the  circuit  the  power  decreases  steadily 
until  at  Troy  it  is  only  3  TU  above  the  origi- 
nal input  at  New  York.  Here  it  is  amplified 
again,  and  continues  on  toward  Syracuse 
The  maintenance  of  a  horizontal  frequency 
characteristic,  the  importance  of  which  has 
already  been  stated,  necessitates  the  introduc- 
tion of  losses  at  the  repeater  points  which  are 
offset  by  amplification;  for  simplicity  these  are 
not  indicated,  the  net  gain  at  each  repeater 
station  being  shown.  The  final  output  power 
of  the  circuit  at  Chicago  is  seen  to  be  four 
times  greater  than  the  input  power  at  New 
York.  The  scale  at  the  right  gives  for  any 
point  the  number  of  TU  by  which  the  power  at 
that  point  exceeds  the  input  to  the  circuit  at 
New  York.  The  left  scale  gives  the  correspond- 
ing power  ratio. 

THE    AMPLIFIERS   OR    "REPEATERS" 

f^\f  COURSE,  the  transmission  of  music  and 
^-'  speech  over  program  circuits  is  by  alternat- 
ing currents  having  frequencies  the  same  as 
those  which  are  present  acoustically  in  the  sound 
at  the  microphone.  So  the  repeaters  in  the  cir- 
cuit are  audio-frequency  amplifiers.  At  the  end 
of  each  program  circuit  in  chain  broadcasting  is 
a  radio  transmitting  station  which  sends  the 
program  out  on  the  ether  at  a  radio  frequency. 

Special  study  has  been  devoted  to  the  design  of 
telephone  repeaters,  and  various  types  have  been 
developed.  Those  used  in  program  circuits  are 
two-stage,  transformer-coupled  amplifiers  using 
130  volts  plate  supply.  The  first  main  element  of 
the  repeater  is  an  input  transformer  whose  sec- 
ondary is  tapped  to  allow  adjustment  of  the 
amplification  given  by  the  repeater.  The  tapped 
voltage  from  this  transformer  is  applied  to  a 
high-mu  tube  having  an  amplification  factor  of 
about  30,  and  an  output  resistance  of  about  60,- 

000  ohms.    From    this    tube   the   energy    goes 
through  an  inter-stage  transformer  to  the  second 
stage.  Here  there  is  a  tube  having  an  amplifica- 
tion factor  of  about  6  and  an  output  resistance 
of   about    6000   ohms,    similar    to    the    2i6-A 
or  1 12  type  tubes  which  have  been  used  in  other 
amplifiers.  There  is  an  output  transformer  for 
delivering  the  amplified  energy  to  the  outgoing 
program  circuit.   Provisions  are  made  for  close 
adjustment  of  amplification  and  for  adjustment 
of  the  frequency  characteristic.  The  amount  of 
amplification  or  "gain"  in  the  repeater  may  bead- 
justed  to  any  value  overa  range  of  37TU  in  steps 
of  as  little  as  0.3  TU  so  that  very  accurate  setting 
is  possible.  At  1000  cycles  this  adjustment  varies 
the  gain  from  5  TU  to  42  TU,  which  is  the  same 
as  varying  the  power  amplification  from  3.2  to 

1  5,800,  or  the  voltage  amplification  from  1. 8  to  126. 

TESTING   AND  OPERATION   OF    PROGRAM   CIRCUITS 

A  FEW  years  ago  the  testing  and  operation  of 
•^  all  the  program  circuits  then  in  use  was  in 
charge  of  one  "transmission  supervisor"  located 
in  New  York.  Since  then,  the  extent  of  program 
circuits  has  grown  by  such  bounds  that  it  has  be- 
come necessary  to  have  additional  transmission 
supervisors,  and  these  are  now  located  at  Boston, 
Cincinnati,  Detroit,  Chicago,  St.  Louis,  Atlanta 
and  San  Francisco.  Each  transmission  supervisor 
is  responsible  for  the  program  circuits  going  out 
from  his  control  point.  He,  therefore,  has  charge 
of  hundreds  of  miles  of  circuits  and  a  number  of 
repeater  stations,  through  which  the  circuits  pass. 
At  each  of  the  repeater  stations  there  are  trained 
men  who  are  on  duty  during  the  hours  that  the 
program  circuits  are  being  tested  or  used,  and 
these  men  make  reports  to  the  transmission  sup- 
ervisor, as  directed,  and  adjust  their  apparatus 
in  accordance  with  his  instructions. 

It  is  very  important  to  maintain  the  prograrr 
circuits  in  the  best  of  condition,  for  manv  thou- 


JUNE,  1928 


HOW  CHAIN  BROADCASTING  IS  ACCOMPLISHED 


67 


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MILES  FROM   NEW  YORK  ALONG  THE  CIRCUIT 


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MAP  SHOWING   ROUTE  OF  CIRCUIT 


WHAT    HAPPENS    TO    ENERGY    IN    WIRE    CIRCUITS 
How  the  voice-frequency  currents  are  attenuated  as  they  travel  over  long 
lengths  of  wire.  Note  the  effect  of  amplification  at  the  repeater  points 


sands  of  radio  listeners  are  dependent  upon  them. 
Each  transmission  supervisor,  therefore,  con- 
ducts every  morning  a  thorough  test  and  ad- 
justment of  all  the  circuits  under  his  charge. 
Transmitting  a  tone  of  1000  cycles  over  the 
program  circuits,  he  receives  reports  by  tele- 
graph and  directs  adjustments  at  the  nearest 
repeater  station,  then  at  the  next  repeater  sta- 
tion, etc.,  until,  in  this  way,  the  entire  group  of 
circuits  under  his  charge  is  "lined  up."  Then  a 
low  frequency,  about  100  cycles  per  second,  is 
transmitted  and  any  necessary  auxiliary  adjust- 
ments are  made  to  see  that  this  low  pitch  is  trans- 
mitted with  the  same  efficiency  as  the  1000 
cycles.  Then  a  high  frequency  of  about  5000 
cycles  is  transmitted  to  check  the  characteristics 
at  this  end  of  the  frequency  range,  and  if  neces- 
sary, appropriate  adjustments  are  made.  Finally, 
music  from  a  phonograph  is  sent  over  the  circuits 
to  give  a  working  check  on  their  condition. 

The  transmission  supervisor  is  also  responsible 
for  the  operation  of  the  program  circuits  during 
use.  As  soon  as  a  report  of  transmission  difficulty 
reaches  him,  he  must  take  immediate  steps  to 
correct  it.  Whether  the  trouble  is  noise  on  the 
circuit  or  low  volume,  he  must  proceed  im- 
mediately with  the  proper  steps.  Sometimes  the 
volume  delivered  by  a  circuit  will  diminish  or 
the  circuit  will  become  noisy  so  as  to  suggest 
approaching  failure.  In  this  case  he  endeavors 
to  obtain  an  alternative  circuit  and  substitute  it; 
sometimes  this  may  be  done  before  the  radio 
listeners  realize  that  any  trouble  has  occurred. 
At  other  times  a  circuit  may,  without  warning, 
fail  completely,  and  at  such  times  the  tians- 
mission  supervisor's  general  knowledge  of  the 
situation  is  put  to  the  test.  He  may  sometimes 
succeed  in  obtaining  an  alternative  circuit  with 
only  three  or  four  minutes  interruption  to  tin 
program.  Sometimes  alternative  circuits  follow 
different  routes  and  far  exceed  in  length  the 
facilities  they  replace,  such  as  during  the  Dem- 
ocratic Convention  in  1924  when  a  connection 
1400  miles  long  was  substituted  in  place  of  one 
only  200  miles  long.  The  transmission  supervisors 
even  keep  informed  of  the  weather  conditions 
over  a  large  part  of  the  country  so  that,  in  case  of 
threatening  storms,  they  may  obtain  emergency 
routes  and  hold  them  in  readiness. 

The  heading  shows  the  program  circuit  control 
point  at  Chicago.  Repeaters,  equalizers,  oscil- 
lators, transmission  measuring  devices,  and  other 
apparatus,  may  be  seen  mounted  at  the  left  and 
in  the  rear.  One  cone  is  connected  to  the  Red 
Network  program,  another  to  the  Blue  Network, 


another  to  the  Purple  Network  (the  Columbia 
Chain),  and  the  fourth  is  a  spare.  In  this  way, 
constant  check  is  kept  on  the  quality  of  the  pro- 
gram transmission.  At  the  right  are  telegraph 
operators  who  transmit  messages  between  the 
transmission  supervisor  and  the  different  re- 
peater stations  under  his  direction. 

NETWORKS    REGULARLY   OPERATING 

THERE  are  now  four  networks  in  daily  opera- 
tion, namely,  the  Red,  Blue  and  Purple  net- 
works in  the  East,  and  the  Pacific  Coast  network 
in  the  West.  The  eastern  networks  are  supplied 
with  studio  programs  from  New  York  City  and 
the  Pacific  Coast  network  from  San  Francisco. 
The  total  length  of  program  circuits  perma- 
nently connected  into  these  four  networks,  or 
connected  on  a  regular  recurring  basis,  was,  on 
April  I,  more  than  15,000  miles.  To  maintain 
and  operate  this  great  amount  of  program  facili- 
ties required  more  than  25,000  miles  of  telegraph 
circuit.  The  daily  audiences  listening  to  the  pro- 
grams from  these  chains  are  estimated  in  the 
millions  of  persons. 

Perhaps  the  reader  has  wondered  how  the 
designation  of  networks  by  colors  originated. 
This  occurred  several  years  ago  when  the  only 
network  then  operating  received  programs  from 


WEAF  in  New  York.  The  telephone  engineers 
drew  in  red  pencil,  on  a  map,  the  circuits  regu- 
larly connected  and  drew  in  blue  the  extensions 
which  were  occasionally  added.  In  this  way  the 
regularly  operating  chain  became  known  as  the 
"  Red  network."  Later,  when  a  network  was 
organized  with  wjz  in  New  York  as  the  key 
station,  the  name  "  Blue  network"  was,  of  course, 
given  to  this.  At  the  important  program  control 
points  the  designation  of  the  networks  by  colors 
is  a  considerable  aid  to  the  transmission  super- 
visor in  the  necessary  switching  operations. 

HISTORICAL    SPECIAL   HOOK-UPS 

ON  DEFENSE  Day,  September  12,  1924,  two- 
way  conversation  between  General  Pershing 
in  Washington  and  the  Commanding  Generals 
of  the  various  •  Corps  Areas  in  New  York, 
Chicago,  San  Francisco  and  other  points  was 
transmitted  to  a  number  of  radio  stations  and 
heard  by  many  thousands  of  listeners.  This 
occasion  remains  an  unbroken  record  for  the 
broadcasting  of  two-way  conversation. 

The  largest  number  of  radio  stations  ever  con- 
nected was  during  the  Radio  Industries  Banquet 
held  in  New  York  on  September  21,  1927,  when 
a  total  of  85  radio  stations  broadcast  the  pro- 
ceedings. All  four  of  the  regular  networks  were 
used  and  13  additional  points  were  added. 

Doubtless  many  readers  will  recall  the  first 
Dodge  Brothers  broadcast  of  January  4,  1928, 
when  well-known  persons  in  Los  Angeles,  New 
Orleans,  New  York,  Chicago  and  Detroit  were 
heard.  The  circuits  used  in  this  broadcast  are 
shown  in  heavy  lines  in  the  drawing  on  this  page, 
totaling  over  20,000  miles  of  circuit,  or  over 
40,000  miles  of  wire.  Other  program  circuits 
operating  on  this  date  but  not  transmitting  the 
Dodge  program  bring  the  total  program  mileage 
to  about  24,000  miles  of  circuit  or  about  48,000 
miles  of  telephone  wire.  In  addition  to  this 
telephone  mileage,  about  40,000  miles  of  tele- 
graph circuit  was  employed  for  lining-up  and 
operating  the  program  circuits.  As  the  pick-up 
point  was  changed  from  one  city  to  another,  the 
circuits  had  to  be  switched  at  correspondingly 
widely  separated  switching-points.  To  perform 
these  operations  in  the  necessary  order  within 
the  allotted  five  seconds  required  thoiough 
training  and  a  high  degree  of  intelligence.  All 
the  pick-up  circuits  not  in  use  for  a  few  minutes 
were  kept  under  continuous  test  to  guard 
against  the  development  of  line  troubles  during 
these  intervals. 


•«*, 


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j  '  **     •'  t 

••-.«,  ,/-  •'         :      MV""*, 


\ 


CHAIN    BROADCASTING    CIRCUITS 
OPERATING    IN    THE    UNITED   STATES 


~-  - 

......   T-  M.<>-,  vtwtrt*-*.  (o       .. 


AT  THE  END  OF  1927 


^  -"  '    . 

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w  •    •  ^S. 


IMFW.N    AND   INTI-.HPHKTATIQN   OF  rtlHHFNT   KADIQ   EVFNTX 

Broadcasting  Needs  Capable  Leadership 


ADIO  broadcasting  is  indeed  a  healthy 
structure  to  survive  successfully  the 
machinations  of  the  politician,  the 
cupidity  of  the  direct  advertiser,  the  absence  of 
articulate  listener  sentiment  and  the  regulation 
of  an  impotent  and  hesitant  administrative 
commission.  Only  its  real  service  to  millions  of 
listeners  gives  broadcasting  its  vitality.  On  every 
hand,  radio  is  the  victim  of  conflicting  interests. 
The  powerful,  well-financed  broadcaster  is  as- 
sailed for  his  supremacy  by  the  less  capable 
station;  the  vote-seeking  politician,  with  a  local 
point  of  view,  hampers  regulation  by  those  who 
understand  frequency  assignment  as  a  scientific 
and  national  problem;  the  ethical  goodwill 
broadcaster  is  tempted  by  the  example  of  the 
blatant  radio  advertiser.  Only  one  influence  can 
lead  the  way  out  of  this  welter  of  confusion  and 
that  is  a  crystallized  listener  sentiment. 

In  its  riotous  career,  broadcasting  has  had 
many  tormentors.  Of  these,  the  most  disturbing 
is  the  belated  and  superfluous  broadcasting 
station  which  has  brought  congestion,  inter- 
ference, and  confusion.  Throughout  its  history, 
broadcasting  has  lacked  capable  independent 
leadership  to  bring  it  through  the  wilderness  of 
uncontrolled  growth.  It  is  illuminating  to  review 
the  causes  of  present-day  congestion  because 
they  point  the  way  to  a  solution. 

When  radio  held  the  center  of  the  stage  of 
public  attention,  the  number  of  stations  grew 
rapidly  to  the  full  capacity  of  the  broadcast 
band.  Room  for  greater  power  and  more  stations 
could  be  gained  only  at  the  cost  of  curtailing 
the  service  of  an  existing  station.  Two  years  ago, 
the  fight  of  one  station  for  another's  time  on  the 
air  upset  the  Department  of  Commerce's  as- 
sumed authority  over  broadcast  regulation, 
which  was  valiantly  stemming  the  rising  tide  of 
stations.  An  effort  was  then  made  to  preserve 
order  by  a  gentleman's  agreement  among  the 
existing  stations.  But  the  success  of  such  a 
course  was  unfortunately  predicated  upon  the 
requirement  that  all  of  those  concerned  be  gentle- 
men. 

During  that  period  of  chaos,  broadcasting 
stations  were  erected  with  reckless  abandon  and 
total  disregard  of  the  capacity  of  the  broadcast 
band.  All  broadcasting  was  conducted  in  a 
bedlam  of  shrill  whistles  and  sullen  groans. 
Stern  parents  punished  their  children  by  making 
them  listen  to  the  radio  nightmare.  But  did  a 
voice,  representative  of  listener  sentiment,  arise 
in  powerful  protest?  Did  any  leader  of  the 
industry  face  the  facts  squarely?  On  the  con- 
trary, the  press  was  flooded  with  statements 
that  there  was  really  nothing  wrong  with  the 
radio  situation.' 

After  several  months  of  torture,  Congress 
began  to  grapple  with  the  situation.  But  did 
anyone  come  forward  with  the  insistent  demand 
that  the  number  of  radio  stations  be  promptly 
and  emphatically  reduced?  The  leaders  of  the 
radio  industry  unremittingly  labored  to  get 
some  kind  of  legislation  passed.  When  debate 
centered  upon  two  forms  of  regulation — by  a 
commission  politically  subservient  to  Congress  or 
by  a  government  bureau  reporting  to  a  cabinet 
officer  and  relatively  free  of  political  instability — 


did  the  industry  declare  itself  squarely  against 
political  regulation?  Indeed  it  did  not;  it  meekly 
favored  both  bills  and,  naturally,  the  bill  giving 
political  influence  the  greatest  sway  became  the 
Radio  Act  of  1927. 

Then  came  the  regime  of  the  Federal  Radio 
Commission.  Did  the  Commission  display  the 
courageous  qualities  of  leadership  essential  to 
success  in  its  onerous  task?  Its  every  act  indicates 
that  internal  strife  vitiated  any  constructive 
measures.  For  six  months,  it  dabbled  with  its 
job.  Credit  must  be  given  for  its  success  in  one 
respect;  the  Commission  did  manage  to  work 
out  the  best  allocation  possible  without  invoking 
the  only  course  which  would  be  successful — the 
elimination  of  excess  stations  in  congested  dis- 
tricts. The  Commission  talked  about  strong-arm 
methods  one  day  and  adopted  weak-kneed 
policies  the  next;  it  announced  that  it  would 
eliminate  300  stations  from  the  broadcast 
spectrum  and  then  promptly  changed  its  mind. 
The  progressive  members  of  the  Commission 
were  invariably  overruled  because  they  could  not 
successfully  face  the  political  pressure  of  Con- 
gressional overlords  who  invariably  backed  the 
weak  against  the  strong. 

When  chivalry  is  applied  to  broadcasting,  it 
means  the  support  of  less  competent  stations 
against  the  so-called  chain  monopoly.  But  to 
what  stations  does  the  listener  turn  his  dials? 


ANCIENT  TRANSMITTING  HISTORY 
Parts  of  the  first  wireless  telegraph  installation 
in  Porto  Rico,  built  for  and  operated  by  the 
United  States  Navy.  The  station  was  located 
near  San  Juan  and  was  completed  in  December 
1903.  The  coil  is  the  antenna  tuning  helix  and 
below  it  is  the  spark  gap  case.  To  the  left  is  the 
box  containing  the  glass  condenser  plates.  The 
spark  gap  was  enclosed  in  the  wooden  box  be- 
cause of  the  terrific  noise  produced 

68 


He  selects  the  powerful  stations  offering  high- 
grade  programs.  As  Representative  Davis  of 
Tennessee  pointed  out,  two  chain  organizations, 
operating  through  seventy-two  stations,  slightly 
more  than  ten  per  cent,  of  the  total  number  of 
stations  on  the  air,  have  50  per  cent,  of  the  total 
broadcasting  power.  The  remaining  stations  on 
the  air  might  be  classed  in  two  groups:  promis- 
ing independents,  offering  high-grade  programs 
and  worthy  of  expansion,  and  the  small,  advertis- 
ing and  propaganda  stations,  which  now  stifle 
the  growth  of  the  better  independents.  The  pre- 
dominance of  the  chain  stations  is  founded  en- 
tirely upon  the  crowding  of  the  more  worthy 
independent  stations  by  the  host  of  worthless 
ether  busybodies.  The  elimination  of  300  small 
stations,  particularly  in  large  cities  where  power- 
ful locals  exist,  would  give  a  well-balanced  struc- 
ture of  chain  and  independent  stations. 

In  all  the  vast  amount  of  conversation  pre- 
cluding the  passage  of  the  amendment  demanding 
equalization  of  broadcasting,  no  one  succinctly 
and  forcefully  stated  the  position  of  the  broad- 
cast listener.  The  villification  of  the  leading 
stations  on  the  air  went  unchallenged.  The 
equalization  amendment  is  a  farcical  grandstand 
play,  which  glibly  overlooks  the  fundamental 
causes  of  concentration  of  stations  in  the  more 
populous  areas.  Merely  to  declare  the  sound 
principle  that  broadcasting  shall  be  geo- 
graphically equalized  will  not  create  the  needed 
stations  in  the  sparsely  populated  areas  or  the 
necessary  channels  so  that  they  might  operate. 

To  equalize  the  power  in  the  five  zones,  only 
three  possible  courses  exist : 

(i)  Power  in  the  weaker  zones  may  be 
increased  so  that  it  equals  that  in  the  more 
progressive  zones;  (2)  power  in  the  strong 
zones  may  be  reduced  to  the  level  of  the 
weaker;  or,  (3)  a  middle  course  between  these 
two  extremes  may  be  adopted. 

Commissioner  Caldwell  showed  that  to  bring 
up  the  power  of  the  weaker  zones  to  that  of  the 
highest  would  require  the  addition  of  276 
stations  with  460,000  watts  power.  Inasmuch 
as  the  broadcasting  band  is  already  hopelessly 
overcrowded,  any  such  increase,  in  fact  any  in- 
crease at  all,  would  bring  nothing  less  than 
chaos.  Averaging  the  present  total  power  among 
the  zones  would  require  a  power  cut  in  the  first 
zone  of  92,000  watts,  curtailing  the  service  of  the 
most  valuable  stations  on  the  air.  At  the  same 
time,  there  are  no  stations  in  the  South  ready  to 
bring  that  section  up  to  average.  Reducing  the 
power  of  all  districts  to  that  available  in  the 
weakest  would  be  wholesale  destruction  of  good 
broadcasting. 

The  broadcasting  industry  should  be  en- 
couraged to  erect  more  great  stations;  the  better 
independents  should  be  given  the  opportunity 
to  serve,  unmarred  by  the  excessive  number  of 
weaklings  on  the  air.  Unless  the  Commission 
develops  an  unlooked-for  independence  and 
courage,  it  will  respond  to  the  temper  of  Congress 
by  hampering  the  growth  of  bigger  and  better 
stations.  What  we  need  is  more,  and  not  less, 
powerful  stations  in  every  section  of  the  country. 
Only  if  listener  sentiment  becomes  suddenly  and 


JUNE,  1918 


BRITAIN  WANTS  PROOF  OF  TELEVISION 


69 


Present  Distribution  of  Broadcast  Stations 


THE  following  is  an  analysis  of  broadcasting 
stations  licensed  as  of  February  29,  showing 
the  inequitable  distribution  of  stations  by  zones. 
Commissioner  Sykes,  representing  the  south- 
ern zone,  has  pointed  out  that  every  legitimate 


request  for  power  increase  and  improved  chan- 
nels, made  by  southern  stations,  has  been 
granted  and  that  the  inequalities  are  due  rather 
to  lack  of  progressiveness  with  respect  to  broad- 
casting in  the  South  than  to  any  discrimination. 


POPL  LAITON 


POPI>  ARE* 

[  ATION  (square 

\ftrcrnl.)          milts') 


AREA         NUMBER  TOTAL 

(ptr  OF  STA-  STATION 

»Y»/.)  TIONS  VOWfiR   IN 

WATT* 


PER- 
CENTAGE 
OF  STA- 
TION 
POWER 


STA- 
TIONS 

WITH 

OVER 

IOOO 

WATTS 


ZotK 

(New  England 
Sts.  N.  1'.  & 

24,378,13' 

22.73 

1  29.769 

363              138 

21.3,055 

3530            10 

N.  J.) 

Zone  2 

(Central  West  & 
Middle  Atlantic) 

24,337.  MI 

22.69 

247017 

h  93              1  1  5 

116,805 

19.34            8 

(Southern) 

24,826,050 

23.14 

761.895 

21    33                   102 

47,105 

7.80              4 

7one  A 

(Northwest) 

24,492.986 

22.83 

658.148 

1*42                   215 

164,870 

27.31            30 

Zone  s 

Western  & 
Pacific  Coast) 

9.2  li,  720 

8.59 

1.774.447 

4.1  h8              Hi 

61.785 

.10,2^                 8 

TOTAL 

l07.248.JiS 

100 

3.571.776 

IOO                         TO  I 

603.620 

100                    60 

immediately  articulate,  and  a  powerful  sweep  of 
opinion  champions  the  two  or  three  hundred 
favorite  stations,  can  the  destructive  effects  of 
the  selfish  and  uninformed  propaganda  of 
Congress  against  good  broadcasting  be  overcome. 

Mergers  in  the  Radio  Industry 

THE  proposed  merger  of  the  Radio  Cor- 
poration and  the  Victor  Talking  Machine 
Company  would  be  a  vital  step  in  bringing 
us  that  combined  broadcast  receiver,  phono- 
graph, home  motion-picture  projector  and  tele- 
vision receiver  which  wej  forecast  in  these  edi- 
torials for  January,  1928,  as  the  ultimate  home 
entertainment  machine.  The  total  assets  of  the 
Victor  Company  are  about  sixty  million  dollars; 
those  of  the  Radio  Corporation  about  sixty-five 
million  dollars.  The  merger  will  make  available 
to  thj  combination  the  services  of  renowned 
artists,  both  for  radio  purposes  and  for  talking 
movies.  The  announcement  that  negotiations 
for  this  merger  were  under  way  was  greeted  with 
the  usual  monopoly  accusations  in  Congress. 
Unquestionably  the  merger  would  result  in  a 
still  stronger  company.  The  consolidation  of 
these  interests  is,  however,  certain  to  enhance 
the  entertainment  value  of  broadcasting  and 
hasten  the  further  development  of  diverse  visual 
and  tonal  amusement  in  the  home. 

Another  merger  of  vital  importance  to  the 
American  radio  industry  is  the  combination  of 
the  Marconi  Wireless  Telegraph  Company  of 
England  with  the  Eastern  Telegraph  Company. 
This  forms  a  one-hundred-million-dollar,  world- 
wide communication  corporation  which  may 
impose  the  pressure  of  severe  competition 
upon  the  Radio  Corporation  of  America.  In 
spite  of  the  comparative  youth  of  the  Radio  Cor- 
ooration,  it  has  become  a  sufficiently  vital  factor 
in  international  communications  to  make  this 
consolidation  of  British  communications  neces- 
sary. 

A  third  merger  which  will  ultimately  affect  the 
radio  communication  business  is  that  of  the 
International  Telephone  &  Telegraph  Company 
A'ith  the  Mackay  interests.  The  former  controls 
telephone  properties  in  Cuba,  Spain,  and  South 
America  and  has  exclusive  rights  for  foreign 
manufacture  of  Western  Electric  Company  prod- 
ucts. The  Mackay  interests  have  an  ambition  to 
set  up  an  international  radio  telegraph  network 
and  may  ultimately  become  serious  rivals  to  the 
Radio  Corporation  of  America.  The  Mackay 
radio  patent  rights  are  based  on  their  acquisition 


of  the  Federal  Telegraph  Company  and  Federal" 
Brandes. 

More  High  Power  Broadcasting 

IT  IS  understood  that  the  Crosley  Radio  Cor- 
poration, operating  WLW,  has  applied  for  a 
50,ooo-watt  assignment  and  that,  like- 
wise, KFI  in  Los  Angeles  is  to  have  a  similar  in- 
crease. The  only  southern  station  to  seek  a 
substantial  power  increase  is  KWKH.  It  is  un- 
fortunate that  some  of  the  more  reputable 
broadcasting  stations  in  the  South  are  not 
aiming  at  substantial  power  increases,  because 
there  are  many  good  reasons  why  KWKH  in 
particular  should  not  be  favored  by  the  Federal 
Radio  Commission.  This  station,  in  plain  de- 
fiance of  the  Commission,  increased  its  power 
surreptitiously  and  utilized  its  facilities  for 
Nullification  of  members  of  the  Commission.  It 
has  established  little  reputation  for  high-grade 
programs,  although  it  is  by  no  means  at  the  bot- 
tom of  the  list  in  that  respect.  We  regret  to  see 
this  progressiveness  for  much  needed  sub- 
stantial power  increases  in  the  South  largely 
confined  to  a  station  which  has  virtually 
thumbed  its  nose  at  the  Federal  Radio  Commfs- 
sion  and  defied  the  simplest  precepts  of  law  and 
order. 


British    Skeptical    of    Baird    Tele- 
vision Accomplishments 

A  PUBLICITY  statement  from  the  Baird 
company  says  that  a  picture  of  Miss 
Dora  Selvey,  transmitted  by  Baird  tele- 
vision from  London  to  the  Berengaria,  a  thou- 
sand miles  at  sea,  was  considered  recognizable 
by  the  radio  operator.  It  must  be  realized  that 
any  kind  of  a  radio  transmission,  which  is  in- 
terpreted by  any  form  of  television  machine, 
makes  some  kind  of  impressions  on  the  screen. 
The  photographs  of  long  distance  television 
reception,  published  in  the  newspapers,  which 
we  have  examined,  have  all  been  faked,  the 
image  drawn  on  the  screen  being  the  work  of 
a  retoucher.  Newspapers,  with  a  nose  for  news, 
however,  do  not  hesitate  to  fool  the  public. 

Popular  Wireless,  a  British  home  constructor's 
magazine,  offers  to  pay  Mr.  Baird  £1000.  if  he 
will  successfully  televise  by  radio,  over  a  dis- 
tance of  not  less  than  twenty-five  yards,  certain 
items  such  as  a  series  of  three  recognizable  faces, 
five  simple  solid  geometric  models  in  slow  mo- 
tion, four  animal  toys,  grouped  and  in  slow  mo- 
tion, and  a  tray,  containing  dice  and  marbles  to  a 
number  not  exceeding  twelve,  all  of  these  objects 
to  be  sufficiently  clear  that  a  committee  of  judges 
can  recognize  them  and  state  their  number.  The 
same  publication  points  out  that  the  television 
sets  being  marketed  in  England,  which  are  not 
true  television  but  shadowgraph  machines, 
require  a  high  voltage  supply  of  six  or  seven 
hundred  volts,  which  is  quite  capable  of  giving  a 
fatal  shock. 

Dr.  Herbert  E.  Ives  of  the  Bell  Laboratories, 
who  demonstrated  the  first  television  appara- 
tus between  Washington  and  New  York  in 
April,  1927,  stated  recently  that  bringing  into  the 
home  by  radio  an  actual  spectacle  like  a  great 
athletic  event  is  unthinkable  because  its  cost 
would  be  simply  enormous.  Television  is  most 
effectively  accomplished  through  wire  lines 
and  displayed  in  theatres  and  auditoriums 
so  that  large  numbers  of  people  will  divide  the 
cost  of  the  presentation. 

WHEN  the  S.  S.  Robert  E.  Lee  ran  on  the 
rocks  while  en  route  from  Boston  to  New 
York  on  March  Q,  several  broadcasting  stations, 
tending  to  interfere  with  the  handling  of  SOS 
traffic,  were  very  slow  in  getting  off  the  air. 
Among  the  stations  named  by  the  Federal 
Radio  Supervisor,  were  wjz,  WRNY,  and  wot. 


©  Harris  &  Ening 
THE  FEDERAL  RADIO  COMMISSION  IS  COMPLETE 

After  long  delay,  the  vacancy  on  the  Commission  was  filled  by  the  President  and  all  the  members 

confirmed  by  the  Senate.  From  lelt  to  right.-  Sam  Pickard,  O.  H.  Caldwell.  Carl  H.  Butman  (secretary). 

I     o   Sykes^  H.  A.  Lafount,  and  I.  E.  Robinson,  chairman 


70 


RADIO  BROADCAST 


JUNE,  1928 


Laxity  in  this  respect  is  rarely  displayed  by  the 
more  important  stations  and  the  lesser,  having 
high-frequency  assignments,  are  least  likely  to 
cause  dangerous  interference.  Since  it  may  be  a 
matter  of  life  and  death,  leniency  to  those  who 
fail  persistently  to  shut  down  promptly  for  dis- 
tress traffic  should  hardly  be  tolerated.  The 
violations  so  far  noted  have  been  only  spasmodic 
and  quite  accidental. 


Here  and  There 


THE  Public  Health  Service  broadcasts,  which 
were  begun    in    1924,   are   now  being    used 
semi-monthly  by  fifty-four  stations.   310   radio 
lectures  have  so  far  been  delivered. 

ASA  result  of  the  forty  per  cent,  reduction 
*•  in  transatlantic  telephone  rates,  there  has 
been  a  fifty  per  cent,  increase  in  the  number  of 
calls  handled. 

\  A /CDA,  a  broadcasting  station  licensed  in 
*  the  New  York  area,  for  some  mysterious 
reason,  after  the  Federal  Radio  Commission 
went  into  operation,  has  sued  WOR  for  $100,000. 
for  an  alleged  harmonic,  attributed  to  WOR, 
which  causes  heterodyne  interference  with  its 
programs.  WOR'S  frequency  is  710  and  that  of 
WCDA  1420.  As  a  matter  of  fact,  two  predominant 
heterodynes  assail  WCDA'S  carrier,  both  of  which 
cannot  be  attributed  to  WOR.  The  technical 
standards,  maintained  by  WOR,  are  beyond  ques- 
tion and  whatever  radiation  there  may  be  on 
its  harmonics,  are  certainly  suppressed  to  the 
minimum  which  the  present  standards  of  the 
radio  art  permit.  Should  WCDA'S  pretentious  suit 
be  successful,  it  would  inevitably  lead  to  other 
suits  because  harmonics  cannot  yet  be  entirely 
avoided.  The  second  harmonic  of  all  stations, 
having  a  fundamental  frequency  lower  than  750 
kilocycles,  falls  in  the  high  frequency  end  of  the 
broadcast  band.  The  successful  prosecution  of 
WCDA'S  suit  would  place  in  jeopardy  all  the 
broadcasting  stations  which  are  assigned  to  fre- 
quencies below  750  kc.  WCDA  should  never  have 
been  given  a  license  in  the  first  place. 

THE    SET    BUILDER    IN    DETROIT 

CARLY  in  April,  manufacturers  of  radio 
*~*  parts  and  accessories  exhibited  at  Conven- 
tion Hall  in  Detroit,  featuring  the  newest  a.  c. 
developments,  units  for  the  use  of  custom-set 
builders,  equipment  for  converting  battery  sets 
to  a.  c.,  parts  for  improvement  of  receiving  sets 
now  in  use.  The  large  attendance  is  indication  of 
the  power  and  numbers  of  the  knights  of  the 
soldering  iron. 

A  JOBBER  section  has  been  formed  by  the 
**  Federal  Radio  Trade  Association.  The 
manufacturers'  relation  committee  of  the 
section  is  headed  by  Harry  Alter,  the  member- 
ship committee  by  J.  M.  Connell. 

RADIO   SALES    IN    FIGURES 

THE  average  business  done  by  radio  jobbers 
is  $218,000  annually,  according  to  figures 
from  a  survey  made  by  the  Electrical  Equipment 
Division  of  the  Department  of  Commerce  and 
the  National  Electrical  Manufacturers'  Associa- 
tion. Three  hundred  and  seventy-five  jobbers  in 
New  York,  New  Jersey  and  Philadelphia  did  an 
average  volume  of  $298,000;  the  New  England 
group  $264,000;  Great  Lakes  region  $240,000 
and  southern  states  $1 18,000. 

Small-town  radio  dealers,  according  to  a  survey 
by  the  same  Bureau,  average  $5200  a  year,  as 
compared  with  $22,800  by  the  average  New  York 
dealers.  The  Philadelphia  average  was  $21,000; 


Chicago  $32,200.  A  group  of  cities,  including 
Boston,  Baltimore,  Cleveland,  Detroit  and  St. 
Louis,  show  an  average  of  $44,300. 

Radio  Retailing  estimates  the  sales  of  radio 
sets  in  1926  at  $506,000,000  and  in  1927  at 
$446,550,000.  Radio  is  now  installed  in  27  per 
cent,  of  American  homes.  If  broadcasting  condi- 
tions are  not  soon  improved,  radio  set  sales 
will  continue  to  decline. 

NO   NEW    IDEAS    IN    PROGRAMS 

COMMENTING  editorially  on  commercial 
^"*  broadcasting,  Editor  fir  Publisher  states: 
"The  rare  incidence  of  new  ideas  in  the  program 
departments  of  large  radio  studios  is  beginning  to 
worry  the  men  assigned  to  the  development  of 
new  converts  in  broadcasting.  The  monotony  is 
beginning  to  pall  on  its  makers  and  the  feeling 
is  expressed  that  the  pall  may  extend  to  the  pay- 
roll unless  expert  direction  is  found  to  steer  pro- 
grams into  new  channels.  ...  As  a  rule,  the  radio 
program  staffs  are  competent  to  provide  a  well- 
balanced  evening  of  entertainment.  They  know 
nothing  of  selling  merchandise  and  the  applica- 
tion of  advertising  to  the  development  of  sales. 
They  have  constructed  a  program  and  stuck 
into  it,  like  splinters  into  a  fruit  cake,  occasional 
mention  of  the  sponsor's  name  and  goods.  The 
advertising  interludes  to  the  entertainment  have, 
in  recent  weeks,  become  more  and  more  blatant." 
Editor  fir  Publisher's  charges  are,  in  the  main, 
true.  There  have  been  very  few  instances  of 
originality  in  the  form  of  program  presentation 
during  the  last  few  years.  One  answer  may  lie 
in  the  fact  that  successful  moving  picture 
directors  get  from  fifty  thousand  to  two  hundred 
thousand  dollars  a  year,  while  the  number  of 
program  directors  in  the  radio  field  who  make 
more  than  five  thousand  dollars  a  yea  an  be 
counted  on  the  fingers  of  two  hands. 

PENDING    SHORT-WAVE    APPLICATIONS 

/^\NE  hundred  and  fifty  applications  for  short- 
*-J  wave  channels  by  new  commercial  and 
public  short-wave  stations,  requiring  350  chan- 
nel assignments,  are  now  pending  before  the 


Federal  Radio  Commission.  Communication 
companies  are  making  45  applications  for  137 
channels;  newspapers  31  for  97  channels;  oil 
companies  28  for  29  channels;  brokerage  houses 
12  for  22;  steamship  companies  7  applications 
for  13  channels;  banking  houses  6  applications 
for  6  channels;  motion  picture  producers  5  ap- 
plications for  10  channels;  rubber  companies  3 
for  4  channels;  coal  i  application  for  2  channels; 
automobile  and  transportation  companies  I 
application  for  i  channel;  and  miscellaneous 
businesses  5  applications  for  7  channels. 

If  these  assignments  are  granted  and  the 
channels  placed  in  use,  the  rivals  of  these  com- 
panies will  also  want  channels  and,  since  further 
channels  will  not  be  available,  the  Federal 
Radio  Commission  will,  of  course,  be  charged 
with  discrimination.  The  principle  of  first  come, 
first  served,  which  must  apply  when  a  limited 
number  of  any  commodity  is  being  dispensed, 
always  carries  in  its  wake  the  cry  of  discrimina- 
tion. 

NEW    AMATEUR    BANDS 

r*  ENERAL  order  No.  24,  by  the  Federal 
^-*  Radio  Commission,  opens  the  2o,ooo-to 
3O,ooo-kc.  band  to  the  amateur.  The  assignments 
are  now  as  follows: 

64,000 — 56,000  kc.  4.69 —  5.35  meters 
3,550 —  3,500  kc.  84.5 —  85.7  meters 
2,000 —  17.5  kc.  150  — 175  meters 

A  SHORT-WAVE  radio  picture  receiver, 
**  installed  on  the  Hamburg  American  liner 
Resolute,  is  said  to  be  successful.  Small  pictures 
and  letters  can  be  sent  for  moderate  distances 
at  a  cost  of  one  dollar. 

THE    NEW   G.    E.    HIGH-FREQUENCY   TUBE 

DR.  W.  R.  WHITNEY  of  the  General 
Electric  Company  recently  described  a 
new  high  power,  high  frequency,  short-wave 
tube,  generating  fifty  million  cycles.  It  radiates 
ten  to  fifteen  kilowatts.  Interesting  psychological 
effects  have  been  noted,  particularly  a  warming 


RADIO  BRIGHTENS  THE  LIFE  OF  OHIO  RIVER   FOLK 

House-boat  dwellers  along  the  Kentucky  shore  of  the  Ohio  River.  The  receiver  is  pulling  in  WGY  and 
is  the  first  radio  reception  these  folk  have  ever  heard.  The  set  was  an  important  part  of  the  equipment 
of  Lewis  R.  Freeman,  member  of  the  Explorers'  Club  of  New  York  who  traveled  from  Pittsburgh  to 
Cairo — a  distance  of  1000  miles  along  the  Ohio  River.  This  set  was  used  to  bring  in  weather  forecasts 
while  navigating  the  river  and  in  one  case,  at  Louisville,  picked  up  a  cyclone  warning,  enabling  Mr. 
Freeman  to  avoid  a  tornado  that  might  have  destroyed  his  expedition 


JUNE,  1928 


NEWS  OF  RADIO  EVERYWHERE 


71 


effect  on  the  blood  of  persons  within  its  influence. 
Small  arcs  are  readily  established  by  metallic 
conductors.  Eggs  and  sausages  have  been  fried 
by  the  heat  generated  on  a  single  wire. 

NEW    RADIO   AVIATION    BEACON 

"THE  visual  indicator,  developed  by  the 
*•  Bureau  of  Standards  of  the  Department  of 
Commerce,  to  show  the  aviator  his  course, 
employs  a  needle-like  reed,  moved  by  electrical 
impulses  received  from  the  radio  beacon  It 
does  away  with  headphones  and  trailing  antenna. 
It  works  on  the  familiar  balanced  signal  principle 
and  gives  indications  for  distances  of  fifty 
miles.  In  mountainous  regions,  however,  its 
directional  accuracy  varies 'but  the  device  should 
be  of  inestimable  help  in  locating  a  landing  field 
through  a  fog  when  the  aviator  is  not  far  distant 
from  the  field.  Guided  by  the  beacon,  he  can 
come  within  range  of  the  fog-penetrating  neon 
light  and  thus  make  a  successful  landing  which 
might  not  be  possible  without  the  radio  direction 
finder. 

QWEN  D.  YOUNG  flatly  stated  recently  that 
the  British  lead  America  in  international 
cable  and  radio  communication.  "The  English 
Government,"  said  Mr.  Young,  "fearing  pre- 
domination of  the  American  radio  group  in  the 
world  of  communication,  has  practically  coerced 
the  interests  in  England  to  combine  cables 
with  radio  in  order  that  the  English  domination 
of  cables  may  continue.  In  America.  Congress 
has  enacted  directly  a  piece  of  legislation  stip- 
ulating that  there  can  be  no  cooperation  or 
relation  between  the  cables  and  radio.  Congress 
had  distintegrated  our  strength  into  small  units 
and  put  each  one  of  them  at  the  mercy  of  a  large 
centralized  foreign  group." 

/^OVERNMENT  officials  in  Czechoslovakia 
^J  estimate  that  the  saturation  point  in  the 
possible  number  of  receiving  set  owners  has 
been  reached  in  that  country  unless  more  broad- 
casting stations  are  erected.  There  are  now 
206,000  listeners  in  Czecho-Slovakia  which  has  a 
population  of  some  thirteen  million. 

D  UMORS  have  appeared  in  the  press  that 
1V  several  large  holders  of  R.  C.  A.  licenses 
have  stopped  payment  on  their  license  contracts 
and  served  notice  to  the  effect  that  at  the 
present  time  they  are  not  able  to  carry  out  their 
agreements  because  of  heavy  declines  in  sales 
and  the  inability  to  realize  on  large  stocks  of 
battery  sets. 

"THE  Brunswick  Phonograph  Company  an- 
'  nounced  that  it  will  place  records  of  certain 
commercial  broadcast  programs  on  the  market 
the  day  following  their  presentation.  It's  bad 
enough  to  hear  most  radio  programs  but  once1 

BRITISH    SHORT-WAVE    EXPERIMENTS 

H  characteristic  caution,  the  British 
broadcasting  monopoly  announces,  through 
its  Chief  Engineer,  Captain  Eckersley,  that 
the  5  sw  high-frequency  transmissions  arc 
being  attempted  largely  to  permit  foreign  and 
dominion  experts  to  ascertain  field  strength  on 
various  frequencies.  "It  would  be  criminal  fool- 
ishness," says  the  announcement,  "to  let  these 
encourage  one  into  saying  that  there  is  yet  a 
guarantee  of  satisfactory  service  worthy  of  the 
object  served." 

International  broadcasting,  through  short- 
wave interconnecting  links,  is  still  a  spectacular 
demonstration  with  all  the  hazards  of  uncer- 
tainty. But  any  new  art  must  begin  in  this  way 
and  the  experiment  should  he  encouraged.  Its 


success  will  accomplish  much  more  than  all  the 
peace  conferences  and  pacifist  disarmament 
propaganda. 

BROADCAST    AREA    SERVED    IN    AUSTRALIA 

"THE  interests  operating  station  3  to  in  Mel- 
1  bourne,  Australia,  have  shown,  by  super- 
imposing a  map  of  Europe  upon  that  of  Aus- 
tralia, that  six  Australian  broadcasting  stations, 
all  fringing  the  coast,  serve  an  area  equal  to 
that  of  Europe,  including  Great  Britain  and  Ire- 
land. Most  of  the  population  of  Australia,  how- 
ever, is  distributed  in  centers  along  the  seacoast. 
There  is  no  problem  of  frequency  shortage  to 
hamper  the  increase  of  broadcasting  stations,  but 
it  appears  that  the  government  authorities 
hesitate  to  permit  an  increase  in  the  number  of 
broadcasting  stations. 

BROADCAST  COOPERATION  IN  EUROPE 

'THE  Union  International  de_  Radiophonie, 
I  which  consists  of  delegates  fium  all  Euro- 
pean countries  operating  broadcasting  stations, 
is  concerning  itself  with  such  problems  as 
frequency  assignments,  accurate  frequency 
measurements  and  the  formulation  of  the  fre- 
quency requirements  of  the  various  nations. 
This  body  serves  the  same  function  as  the 
Federal  Radio  Commission  in  the  United 
States,  except  that  it  has  no 'legal  authority 
and  must  settle  its  affairs  by  mutual  agreement 
and  conference. 

pCJJ,  the  Dutch  short-wave  broadcasting 
station,  frequently  heard  by  American 
enthusiasts,  has  adopted  a  schedule  as  follows: 
Tuesdays  and  Thursdays,  16  to  19  Greenwich 
mean  time,  and  Saturdays  14  to  17  G.  M.  T. 

A  USTRIA  now  claims  to  be  the  most  pro- 
gressive country  in  the  broadcasting  field, 
so  far  as  percentage  of  registered  listeners  is  con- 
cerned. 300,000  out  of  its  6,500,000  population 
are  registered  radio  listeners.  Radio  manufactur- 
ing is  also  developing  rapidly,  exports  being 
four  times  greater  than  imports. 


FACSIMILE    TRANSMISSION    USED 


THE  extent  to  which  financial  enterprise  is 
1  utilizing  the  modern  means  of  electrical 
communication  is  illustrated  by  the  recent  float- 
ing of  ten  million  dollars  in  bonds  for  Warsaw, 
Poland,  simultaneously  in  Europe  and  America. 
A  1400-word  descriptive  circular  was  compiled 
and  sent  by  radio  to  London  and  Stockholm. 
Quarter-page  ads  were  then  set  up.  in  London 
and  mats  made  and  distributed  by  air  mail  to 
other  European  capitals.  The  circular  was 
cabled  to  South  America  and  put  into  type.  In 
New  York,  it  was  set  up  and  distributed  by 
telephoto  to  cities  as  far  west  as  the  Pacific 
Coast.  Thus  transatlantic  radio  picture  circuits, 
airplanes,  telephoto,  and  cable  were  used  in  this 
international  financial  venture. 

THE  transatlantic  telephone  service  was  ex- 
tended to  Belgium  on  January  19  and  to  Holland 
on  January  30. 

HERBERT  H.  FROST,  formerly  General  Sales 
Manager  of  E.  T.  Cunningham,  Incorporated, 
has  resigned  to  become  Vice-President  of  Federal- 
Brandes,  Incorporated. 

D  ADIO  beacon  service  is  to  be  installed  along 
I  v  the  French  coast.  One  station  is  to  be  built 
at  the  mouth  of  Cherbourg  harbor  and  another 
ten  miles  northeast  of  that  point  so  that  bear- 
ings can  be  given  to  incoming  ships. 

A  DECISION  of  the  U.  S.  District  Court  in 
Cincinnati  declares  that  the  Crosley  Musi- 
cone  does  not  infringe  upon  the  Lektophone 
patents.  The  Musicone,  says  the  decision,  is 
drawn  from  the  same  prior  art  that  the  Hopkins 
invention  is  made  and  is  an  improvement  thereof. 
The  Supreme  Court  of  Canada  holds  that  the 
patent  granted  by  the  United  States  to  the 
German  inventors  Schoelmich  and  Von  Bronk 
is  prior  art  over  the  Alexanderson  tuned  radio 
frequency  patent.  This  is  directly  opposite  to 
the  opinions  of  American  courts. 

— F.  H.  F. 


RADIO  CABIN  OF  THE  MOTORSHIP  "BERMUDA" 

This  is  the  latest  type  Marconi  installation  for  ships  and  shows  (left  to  right)  gvro-compass  repeater 
•Ltion  finder;  receiver  operatmg  on  all  wavelengths  from  300-20,000  meters    'kwo       ctad 
spark  transrm.ter;  ,1-kw.  c.w.  and  i.c.w.  tube  transmitter  working  between  f^   ami  2^.0  meters 


By  LEROY  S.  HUBBELL 


IF  WE  review  the  development  of  the  me- 
chanics of  a  radio  receiving  set  we  remember 
a  panel  resembling  a  small  switchboard 
which  had  primary  and  secondary  inductance 
switches,  an  A  battery  control  switch,  several 
variable  condenser  controls  and  other  minor  con- 
trol switches.  Gradually,  over  several  years, 
these  numerous  controls  began  to  disappear 
until  now,  on  the  panels  of  many  of  the  recent 
designs,  not  more  than  three  controls  exist, 
namely,  the  on-off  switch,  a  single  dial  for  con- 
trolling the  variable  condensers,  and  sometimes 
a  volume  control. 

While  there  have  been  many  improvements 
toward  simplifying  the  tuning  of  a  radio  receiver, 
it  is  still  necessary  to  manipulate  a  dial  and  if 
a  particular  station  is  desired  it  is  necessary 
to  consult  a  schedule.  If  no  tuning  schedule  is 
available  the  settings  are  oftentimes  haphazard. 
In  a  large  number  of  cases,  particularly  in  the 
metropolitan  areas,  the  dial  settings  are  usually 
confined  to  not  more  than  five  to  ten  stations. 
When  one  is  comfortably  seated,  whether  in  a 
favorite  armchair  by  the  fireside  or  at  the  table 
enjoying  a  dinner  or  participating  in  a  card 
game  it  is  annoying  to  interrupt  one's  activity  to 
adjust  the  radio  to  some  other  station  in  search 
of  a  more  delectable  program.  The  partial  elimi- 
nation of  the  multi-controls  on  the  radio  receiver 
has  reduced  immensely  the  trials  and  tribulations 
of  many  a  lover  of  radio  entertainment.  Probably 
there  will  always  be  at  least  two  controls,  one 
for  the  station  setting  and  another  for  the  volume 
from  the  loud  speaker.  Take  these  two  controls 
to  the  armchair  by  the  fireside  or  to  the  table  and 
the  ideal  radio  entertainment  is  at  hand. 

In  this  article  we  discuss  a  means  for  auto- 
matically tuning  a  radio  receiver  at  a  remote 
point,  although  the  same  equipment  may  be 
used  in  connection  with  a  transmitting  station 
where  the  tuning  elements  are  adjustable.  The 
advantages  may  be  summarized  as  follows. 

1.  The  set  may  be  tuned  to  any  one  of 
several  definite  stations  by  pressing  a  button. 

2.  The  set  may  be  controlled  at  any  point 
of  convenience. 

}.  The  radio  receiver  may  be  housed  in  a 
closet  or  other  out-of-way  place  reducing 
considerably  the  cost  of  expensive  furniture. 

4.  An  outdoor  directional  loop  type  an- 
tenna may  be  used  instead  of  the  present 
antenna. 

[Judged  by  present  standards,  Mr.  HubbelPs 
automatic  tuning  mechanism  has  certain  draw- 
backs, as  well  as  obvious  advantages.  These 
limitations  hold  for  all  automatic  tuning  me- 
chanisms with  which  we  are  familiar.  The  appar- 
atus takes  up  considerable  space,  and  although, 
as  Mr.  Hubbell  suggests,  the  receiver  and  the 
tuning  mechanism  may  be  located  elsewhere 
than  in  the  living  room  or  the  den — or  wherever 
receivers  now  in  common  use  are  located — it  is 
necessary  to  place  the  automatic  mechanism 
quite  close  to  the  radio  apparatus  and  in  most 
cases  that  involves  rearranging  at  least  the  radio 
frequency  and  detector  circuits  of  the  receiver. 
Neither  Mr.  Hubbell's  arrangement  or  any  other 
can  readily  be  applied  to  the  average  existing 
receiver.  That  is,  of  course,  not  a  serious  disad- 
vantage, for  it  is  not  difficult  to  rearrange  a 
"pet  circuit"  so  that  the  relay  tuning  controls 
are  operative.  Cost,  too,  is  a  factor,  but  a  very 
real  gain  in  convenience  is  achieved  which  should 
equalize  that. — Editor.] 


AN  EXPERIMENTAL  SET-UP  OF  THE  HUBBELL  AUTOMATIC  TUNING  CONTROL 

The  photograph  shows  a  rough  model  of  the  tuning  control  apparatus  and  the  radio  and  detector  circuits 

of  the  receiver.  The  motor  in  this  illustration  is  much  larger  than  necessary.  The  model  shown  is  equipped 

for  tuning  only  to  one  broadcast  station.  For  each  additional  station,  two  more  cams,  one  on  each  shaft 

will  be  required  and  one  additional  relay  for  each  station 


THE    APPARATUS    USED 

THE  equipment  designed  by  the  author  for 
automatically  tuning  radio  apparatus  con- 
sists essentially  of  a  small  commercial  type  motor 
of  about  6>0-  h.p.  or  less,  depending  on  the  num- 
ber of  stations  the  equipment  must  tune  to, 
connected  to  a  revolving  iron  disc  through  a  re- 
duction gear.  The  revolving  iron  disc  is  caused  to 
engage  at  right  angles  another  iron  disc  by  means 
of  an  electro-magnet  (magnetic  clutch).  The 
second  disc  is  connected  to  a  series  of  cams  to 
which  spring  contacts  engage.  Two  cams,  one 
acting  as  a  vernier  to  the  other  and  a  relay  are 


OF  LATE  there  has  been  a  considerable  interest 
in  the  automatic  tuning  of  radio  receivers. 
Remote  tuning  control  of  radio  transmitters  has 
been  used  for  some  time,  in  various  forms  by  both 
commercial  and  military  radio  stations,  but  until 
recently,  little  bad  been  done  to  explore  the  possibil- 
ities in  the  radio  receiver.  This  timely  article  by 
Mr.  Hubbell  describes  the  mechanical  principles 
of  the  system  which  he  has  devised;  the  illustrations 
show  a  rough  model.  A  commercial  model  would 
probably  be  quite  different  in  arrangement  and 
appearance.  Practically,  the  device  suggested  by 
Mr.  Hubbell  is  limited  to  the  control  of  from  ten  to 
fifteen  stations,  but  it  does  permit  the  manual  con- 
trol of  the  receiver  at  any  time.  No  effort  has  been 
made  to  treat  this  subject  from  the  constructional 
point  of  view.  Our  readers  will  nevertheless  be  in- 
terested in  the  description  of  the  present  method. 
All  patent  rights  are  reserved  by  the  author. 

— THE  EDITOR. 


required  for  each  wavelength  setting.  If  the  radio 
apparatus  has  more  than  one  variable  control 
the  clutch  and  cams  are  duplicated,  but  the 
motor  and  reduction  gear  are  common  to  any 
number  of  controls. 

At  a  distance  from  the  radio  set  there  is  a 
small  button  box  which  contains  a  button  for 
each  wavelength  and  associated  with  each  button 
is  a  small  display  lamp  to  indicate  the  station 
to  which  the  set  is  tuned.  The  button  box  also 
contains  a  rheostat  or  potentiometer  for  con- 
trolling the  volume  at  the  loud  speaker. 

Except  for  the  push  buttons,  display  lamps 
and  volume  control  switch,  the  tuning  mechan- 
ism may  be  housed  within  the  radio  cabinet. 
For  those  who  are  not  interested  in  distant 
stations  and  confine  their  entertainment  to  local 
broadcast  programs  it  would  be  practical  and 
desirable  to  place  the  radio  equipment  in  a 
closet  or  other  out-of-sight  place  thus  reducing 
the  cost  of  the  receiver. 

In  the  accompanying  Fig.  i  is  shown  the 
fundamentals  underlying  the  operation  of  the 
automatic  tuning  equipment  designed  by  the 
author.  In  the  lower  left  hand  side  of  tht-  draw- 
ing is  shown  a  revolving  iron  disc,  Dj.  whose 
shaft  is  connected  '  to  a  small  motor  (not 
shown)  through  a  reduction  gear.  When  the 
motor  is  energized,  the  iron  disc  to  which  it  is 
connected  revolves  at  about  60  revolutions  per 
minute.  Adjacent  to  this  disc  is  another  iron 
disc,  D«,  the  axis  of  which  is  at  right  angles  to 
the  former.  These  two  discs  have  about  //'  clear- 
ance between  their  edges.  There  is  a  magnet, 
Mi,  mounted  closely  against  the  driving  disc, 
but  not  touching  it,  with  one  of  its  poles  facing 
the  driven  disc.  There  is  a  return  pole  piece  on 


JUNE,  1928 


AUTOMATIC  TUNING  FOR  THE  RADIO  RECEIVER 


73 


the  magnet  to  concentrate  the  flux  at  the  driven 
disc  end.  On  the  driven  disc  there  is  mounted  a 
six-fingered  suspension  spring  which  connects  at 
its  center  the  shaft,  S,  to  the  driven  disc  at  the 
extremities  of  the  fingers.  This  spring  permits 
the  driven  disc  to  hold  up  against  the  driving 
disc  when  the  magnet  is  energized. 

On  the  shaft,  S,  a  cam  is  mounted  consisting  of 
copper  punchings  riveted  to  a  fiber  disc.  The 
front  of  the  cam  is  shown  in  perspective  while 
the  rear  of  the  same  cam  is  shown  at  the  right 
of  the  drawing  in  full  view.  On  the  front  of  the 
cam  it  will  be  noted  that  the  copper  punchings 
are  cut  so  that  the  brushes  resting  against  the 
cam  pass  over  segments  and  interrupt  any 
current  which  may  be  passing  through  the 
brushes.  On  the  rear  of  the  cam  there  are  no 
breaks  in  the  copper  punchings.  These  copper 
punchings  are  electrically  connected  to  the 
punchings  on  the  front  of  the  cam  by  rivets.  In 
the  upper  portion  of  the  drawing  a  conventional 
relay  is  shown.  In  the  lower  right  hand  side  a 
push  button  and  a  display  lamp  is  indicated. 
The  shaft,  S,  is  connected  to  the  proper  variable 
tuning  element  of  the  radio  set  such  as  a  variable 
condenser,  a  variometer,  etc. 

TUNING    FOR    STATIONS 

BY  PRESSING  the  push  button  a  circuit  is 
closed  beginning  with  the  ground  side  of  the 
battery  through  the  contacts  of  the  push  button, 
and  the  relay  to  battery.  The  relay  operates  and 
in  so  doing  establishes  a  circuit  to  lock  itself  up. 
The  circuit  is  as  follows:  beginning  with  ground 
at  the  left  of  the  relay  through  the  making  con- 
tacts to  the  upper  spring  pressing  against  the  rear 
of  the  cam,  through  the  rivets  of  the  cam  to  the 
upper  brush  on  the  front  of  the  cam  back  to  the 
right  hand  contact  spring  of  the  relay,  through 
the  winding  of  the  relay  to  battery. 

At  the  same  time  that  ground  is  connected  to 
the  upper  brush  on  the  front  of  the  cam.  a 
ground  is  placed  on  the  middle  brush  which 
operates  the  magnet.  Also  a  ground  is  supplied 
to  the  motor  lead  which  operates  a  relay  in  the 
motor  circuit  causing  the  motor  to  rotate.  The 
shaft.  S,  now  rotates  and  continues  to  rotate 
until  the  top  and  middle  brush  fall  into  the 
open-shaded  segment  of  the  cam.  The  set 
screw,  A  on  the  cam  huh  permits  the  cam  to 
be  set  at  any  angular  adjustment  so  that  the 
variable  element  in  the  radio  set  can  be  rotated 
to  any  predetermined  selling.  In  practice  there  is 
another  shaft,  S»  (see  the  accompanying  illus- 
trations) paralleling  the  shaft,  S,  on  which  is 
mounted  a  similar  cam  and  brushes.  The  second 
shaft  is  connected  to  shaft  S,  through  a  gear, 
reducing  the  speed  from  60  r.p.m.  to  3  r.p.m. 
The  brushes  of  the  second  cam  are  connected 
in  multiple  with  the  brushes  shown  so  that  by 
connecting  the  variable  condenser  or  other 
variable  element  to  the  second  shaft,  a  micro- 
meter adjustment  is  obtainable. 

When  the  cam  on  shaft  S  has  arrived  at  the 
break  in  the  copper  punching  the  circuit  to  the 
motor,  clutch  and  relay  is  opened.  A  contact  is 
made  however  on  the  lower  brush  at  both  sides 
of  the  cam  which  completes  a  circuit  from  the 
ground  at  the  relay  (the  relay  now  being  re- 
leased) through  the  lower  brushes  on  both  the 
front  and  rear  of  the  cam  through  the  display 
lamp  to  battery.  The  display  lamp  is  lighted  to 
indicate  that  the  variable  element  in  the  radio 
receiver  is  tuned  to  a  wavelength  as  predeter- 
mined by  the  adjustment  of  the  cam  on  shaft  S. 

It  should  be  noted  that  the  lead  marked  "To 
battery  switch"  is  connected  to  battery  through 
the  released  contacts  of  the  relay.  With  this  ar- 
rangement all  undesirable  noises  in  the  loud 
speaker  are  eliminated  when  the  variable  ele- 
ments are  passing  over  unwanted  stations.  As 


A    SIDE    VIEW    OF    THE    EXPERIMENTAL    UNIT 
This  illustration  shows  the  mechanical  relation  of  the  reduction  pulley  and  the  main  shaft,  Sj 


soon  as  the  cam  has  arrived  at  its  predetermined 
station  setting  the  relay  releases  and  through  its 
contacts  supplies  current  over  lead  "To  battery 
switch"  to  the  A  battery  rheostat 

The  push  button  and  display  lamp  indicated 
in  the  drawing  together  with  a  plurality  of  push 
buttons  and  lamps  are  mounted  in  a  button  box 
away  from  the  tuning  equipment,  the  latter  as 
suggested  above  are  housed  within  the  radio 
cabinet.  From  the  push  button  box  there  are 
two  wires  for  each  button,  a  pair  for  the  two 
poles  of  the  battery  and  a  lead  for  controlling 
the  volume  at  the  loud  speaker.  For  a  six-station 
controlled  set,  there  would  be  about  15  wires  in 
a  flexible  silk  covered  cable  leading  from  the 
position  of  the  button  box  to  the  radio  set. 

The  relays  used  are  of  commercial  manufac- 
ture having  resistances  of  approximately  200 
ohms  and  operating  on  6  volts.  The  magnet  is 
part  of  the  construction  of  the  tuning  mechanism 
and  is  wound  to  operate  on  a  6-volt  battery  at 
about  15  watts.  The  battery  used  may  be  either 
a  loo-ampere  storage  battery  or  may  be  replaced 
by  an  a.c.  rectifier  which  would  operate  only 
when  required.  Low  voltage  a.c.  for  operating 
the  relay  and  lighting  the  display  lamp  would 
also  be  required  if  the  storage  battery  is  elimin- 
ated. 

In  the  photographs,  the  relays  referred  to  and 
the  magnetic  clutch  are  marked.  The  motor, 
which  rotates  at  about  1750  r.p.m.  is  connected 
to  the  device  by  means  of  a  belt.  Between  the 
motor  shaft  and  the  driving  disc  shaft  the  speed 
is  reduced  to  about  60  r.p.m.  through  the  pulleys 
on  both  the  motor  and  the  device  and  the  re- 
duction gears  on  the  device  itself.  The  mag- 
netic clutch  being  energized  by  the  relay  as 
mentioned  above,  is  holding  the  driven  disc 
up  against  the  driving  disc  causing  the  cam  on 


To  Motor  •» 


To  Battery  Switch 

Battery 

or 
A.C.  Rectifier 


the  left  hand  shaft  to  revolve  clockwise  and  the 
cam  on  the  opposite  shaft  to  revolve  counter 
clockwise. 

The  cam  on  the  left  hand  shaft  revolves  at 
about  60  r.p.m.  while  the  cam  on  the  right  hand 
revolves  about  3  r.p.m.  the  reduction  taking  place 
through  the  gears  connecting  the  two  shafts. 

1 1  will  be  noted  that  the  tuning  device  and  the 
variable  condensers  are  not  directly  connected. 
The  means  shown  permits  a  free  movement  of 
the  condensers  through  nearly  360  degrees.  By 
this  feature  it  is  possible  to  tune  the  radio  set 
manually  to  any  desired  station  free  of  the  auto- 
matic tuning  device.  The  experimental  model  is 
equipped  to  tune-in  automatically  only  one 
broadcast  station,  that  station  being  dependent 
upon  the  settings  of  the  two  cams.  For  each 
additional  station  two  more  cams,  one  on  each 
shaft  will  be  required.  One  additional  relay  will 
also  be  required  for  each  additional  station.  The 
practical  limit  is  probably  about  10  or  15 
stations. 

For  cases  where  there  is  another  adjustable 
tuning  element  in  the  radio  set  and  which  can 
not  be  directly  connected  to  a  single  control,  it 
is  possible  to  tune  automatically  that  element 
independently.  To  do  this  a  shaft  is  extended  to 
another  device  which  is  similar  to  that  shown. 
In  this  case,  however,  the  only  parts  which  re- 
quire duplication  are  the  cams  and  magnetic 
clutch  and  the  spur  gears  which  connect  the 
upper  shaft  to  the  driving  disc  shaft. 

The  second  relay  shown  in  the  photographs  is 
connected  between  the  push  button  relay  (shown 
in  diagramatic  form  in  Fig.  i)  and  the  motor. 
The  use  of  this  relay  merely  separates  the  direct 
current  circuit  used  to  operate  the  radio  set 
trom  the  i  lo-volt  alternating  current  lighting 
circuit  which  is  used  to  operate  the  motor. 


FIG.     I 

Schematic    diagram 
of    a     method     for  Ma8"et 
automatic    tuning        I"  1 
control  of  a  radio  re- 
ceiver.  The    parts 
labeled   are  referred 
to  in  the  text 


Rivets  connecting 
oth  sides  of  Cam 


Disc  suspended 
suspension  spri 

toShaft"S"       Pash/ 


Rear  view 
'of  Cam 


Display  Lamp 
Through  Battery  Switch 


"-Shaft  connected  to  Motor 
or  other  driving  power  through 
Reduction  Gear 


THE  NEWEST  POWER  TUBE 

By  Howard  E.  Rhodes 


Radio  Broadcast  Laboratory 


PLATE 
VOLTAGE 


THH   UX-2JO  (cx-j5o)    "special    purpose" 
tube  is  the  newest  and  probably  the  last 
of  the  line  of  power  amplifier  tubes  de- 
signed for  use  with  radio  receivers,  for  according 
to  its  designers,  the  power  output  is  about  as 
large  as  may  be  obtained  from  a  tube  mounted 
in  a  standard   receiving  tube  base.  The  glass 
bulb  enclosing  this  tube,  which  determines  the 
amount  of  heat  that  can  be  dissipated,   is  as 
large  as  is  feasible  using  this  base. 

To  what  use  can  this  power  tube  be  put?  What 
advantages  and  disadvantages  has  it  over  other 
types?  Let  us  compare  it  with  others  to  get  a 
clear  picture  of  the  relation  between  the  250 
and  other  tubes. 

Fig.  I  shows  how  the  power  output  of  this 
tube  compares  with  that  of  the  other  types  of 
power  tubes  at  various  plate  voltages. 

TABLE  I 

UNDISTORTED  POWER  OUTPUT  IN  MILLI- 
WATTS 

112  171  210  250 

90  40  130 

135  120  330 

157  195  500  90 

180  700  140 

250  340  900 

350  925  2350 

400  1320  3250 

450  1760  4650 

The  figures  in  Table  I  together  with  data  on 
several  push-pull  combinations  have  been 
plotted  in  Fig.  i.  This  graphic  representation 
of  the  power  output  of  various  tubes  and  com- 
binations of  tubes,  as  a  function  of  plate  volt- 
age, serves  well  to  illustrate  the  relative  position 
of  each  tube  from  the  standpoint  of  power  out- 
put. 

When  interpreting  these  curves,  it  should  be 
appreciated  that  a  considerable  increase  of  power 
output  is  necessary  in  order  to  make  the  effect 
appreciable  to  the  ear.  Twice  the  power  output  is 
equivalent  to  an  increase  of  3  TU  which  is  not 
very  great,  i  TU  being  a  just  audible  increase. 
It  is  necessary  that  the  available  power  be  in- 
creased two  or  three  times  in  order  for  the  in- 
crease to  be  worth  while. 

The  choice  of  which  type  of  tube  is  used  de- 
pends, obviously  upon  how  much  power  output 
is  desired.  If  not  more  than  200  milliwatts  are 
required,  the  1 12  may  be  used ;  for  a  power  output 
up  to  700  milliwatts  the  171  type  tube  is  used. 
If  greater  power  than  this  is  required  we  can  use 
either  a  210  or  a  250  type  tube.  A  more  detailed 
analysis  of  these  two  tubes,  showing  how  their 
power  output  varies  with  the  applied  plate  volt- 
age is  given  below. 

POWER  OUTPUT  OF  210  TUBE 

PLATE              POWER  PLATE  GRID 

VOLTAGE           OUTPUT  CURRENT  BIAS 

(Milliwatts)  (mA)  (volts) 

250                      340  10  18 

350                      340  16  27 

450                   1700  18  39 

POWER  OUTPUT  OF  250  TUBE 

PLATE                      POWER  PLATE  GRID 

VOLTAGE                 OUTPUT  CURRENT  BIAS 

(Milliwatts)  (mA)  (volts) 

250           900  28       45 

350           2350  45       63 

450      .     4650  55       84 


This  table  is  very  interesting  for  it  shows  that 
at  all  plate  voltages,  the  250  tube  is  capable  of 
delivering  more  than  twice  the  power  output  of  a 
210  tube.  For  use  in  a  straight  amplifier  (not 
push-pull)  the  tube,  from  the  analysis  given 
above,  seems  to  be  much  the  best  for  it  is  capable 
of  delivering  much  more  power  than  any  other 
type  of  tube.  When  operated  at  maximum  volt- 
age, the  250  can  deliver  a  power  output  of  4.6 
watts  which  is  about  as  much  as  can  be  obtained 
from  two  210  type  tubes  in  push-pull.  In  the 
following  paragraphs  a  more  complete  compari- 
son is  given  of  a  single  2501'$.  2io's  in  push-pull. 

POWER    SUPPLY    EQUIPMENT 

A  BOUT  450  volts  are  required  in  both  cases 
**  and  the  plate  current  requirements  (about 
40  mA.  for  2io's  in  push-pull  and  55  mA.  for  a 
single  250)  are  not  sufficiently  different  to  make 
the  power  supply  equipment  much  cheaper  for 
one  of  the  two  arrangements.  In  so  far  as  the 
power  supply  is  concerned,  therefore,  there  is  no 
distinct  advantage  in  favor  of  a  single  250  rather 
than  two  2io's  in  push-pull  or  vice  versa. 

A    COMPARISON    OF   COST 

SINCE  ordinary  transformers  are  cheaper 
than  push-pull  transformers  it  is  somewhat 
less  expensive  to  construct  a  power  amplifier 
using  a  single  250  type  tube  than  two  2io's  in 
push-pull.  For  example,  suppose  that  trans- 
formers costing  about  as  much  as  Amertran's 
were  to  be  used  in  the  amplifier, 

SINGLE  250  TUBE 

Input  transformer $10.00 

Output  device        10.00 

One  250  type  tube 12.00 

One  socket 1.00 

Total                                                             .  $33.00 


210'S  IN  PUSH-PULL 

Input  transformer 

Output  transformer 

Two  210  type  tubes 

Two  sockets 

Total 


$15.00 
15.00 
18.00 
2.00 

$50.00 


FIG.     I 

How  the  power  output  of  the  250  type  power 

tube  compares  with  other  types  of  power  tubes, 

at  various  plate  voltages 

74 


Here  we  see  a  distinct  advantage  in  favor  of 
a  power  amplifier  using  a  single  250  tube  and 
delivering  to  the  load  about  as  much  power  as 
2io's  in  push-pull,  which  will  cost  only  about 
65  per  cent,  as  much  as  a  push-pull  amplifier. 

A    COMPARISON    OF   QUALITY 

IN  THIS  characteristic,  the  push-pull  arrange- 
'  ment  is  theoretically  better  than  the  single 
tube  because  the  former  arrangement  eliminates 
second  harmonic  currents — currents  which  rep- 
resent distortion  and  which  are  passed  on  to 
the  loud  speaker  when  only  a  single  tube  is  used. 
However,  even  with  a  single  low-plate-im- 
pedance tube  such  as  the  250,  there  isn't  much 
second  harmonic  current  generated  by  the  tube 
in  the  load  circuit  when  the  tube  is  delivering 
its  rated  power,  or  less  for  under  the  condition 
that  the  tube  is  working  into  a  load  impedance 
approximately  twice  as  great  as  the  tube's  plate 
impedance  the  amount  of  second  harmonic 
current  in  the  output  is  not  greater  than  5  per 
cent. — an  amount  of  distortion  which  is  con- 
sidered small  enough  not  to  be  appreciable  to 
the  ear.  If  the  load  impedance  is  smaller  than 
twice  the  tube's  impedance,  there  is  more  dis- 
tortion; if  it  is  equal  to  the  tube's  impedance, 
the  amount  of  distortion  due  to  second  harmonic 
currents  will  be  about  15  per  cent.,  this  latter 
figure  being  calculated  from  some  curves  on  the 
tube  to  be  published  in  the  Proceedings  oj  the  I. 
R.  E.  ("Development  of  a  New  Power  Am- 
plifier Tube,"  Hanna,  Sutherlin,  and  Upp).  The 
impedance  of  many  loud  speakers,  at  the  very 
low  frequencies,  will  be  about  the  same  as  that 
of  the  250  type  tube  (2000  ohms)  and  therefore 
there  will  be  about  15  per  cent,  second  harmonic 
current  generated  by  the  tube.  However,  the 
sounds  created  by  musical  instruments  contain 
many  harmonics  and  the  ear  itself  probably 
generates  others,  so  it  may  be  that  the  above 
figure  of  distortion  is  not  large  enough  to  be 
serious. 

The  210  push-pull  arrangement  has  an  ad- 
vantage over  the  single  250  when  the  filaments 
are  to  be  operated  on  raw  a.  c.  In  the  push-pull 
amplifier,  any  hum  due  to  the  a.  c.  operation  of 
the  filaments  is  cancelled  out,  while  with  the 
single  tube  arrangement  this  does  not  occur. 
However,  the  250  tube  uses  a  heavy  ribbon  type 
filament  (similar  to  that  used  in  the  280  type 
tube)  which  has  a  high  thermal  inertia  tending 
to  prevent  the  production  of  any  a.  c.  hum  when 
its  filament  is  operated  on  raw  a.  c.  The  250  type 
has  a  low  plate  impedance,  (about  1800  ohms) 
and  can  therefore  be  used  with  ordinary  loud 
speakers  without  any  need  of  an  impedance- 
adjusting  transformer.  Two  2io's  in  push-pull 
have  a  plate  impedance  of  about  10,000  ohms 
and  in  this  case  it  is  best  to  use  an  impedance- 


JUNE,  1928 


THE  NEWEST  POWER  TUBE 


75 


adjusting  output  transformer  to  adapt  the  tube 
impedance  to  that  of  the  loud  speaker.  Although 
an  impedance  adjustment  is  not  necessary  when 
using  a  250  type  tube,  it  is  necessary  to  use  an 
output  device  to  protect  the  windings  of  the 
loud  speaker  from  the  high  plate  current  of  the 
250  tube. 

COMPARISON    OF    SENSITIVITY 

UNDER  this  caption  we  discuss  how  the  two 
arrangements  compare  with  regard  to 
power  output  for  a  given  input  voltage.  Let  us, 
therefore,  calculate  the  power  output,  fora  given 
input,  for  both  arrangements.  If  each  arrange- 
ment works  into  a  load  impedance  equal  to 
twice  fhe  tube  impedance,  then,  per  volt  input 
squared,  there  will  appear  in  the  load  the 
amounts  of  power,  as  indicated  below. 

ARRANGEMENT  POWER    IN    LOAD.    PER 

VOLT  SQUARED,  ON  GRID 

OF  TUBE 
0.8  milliwatts 
3.0  milliwatts 


Single  250 
Push-pull  210's 


In  this  table  the  250  shows  up  very  poorly, 
being  only  about  one-quarter  as  sensitive  as 
2io's  in  push-pull.  However,  the  turns  ratio 
of  the  average  push-pull  input  transformer 
available  to-day  is  lower  than  an  ordinary  trans- 
former and  if  we  assume  that  with  a  single  tube 
the  input  transformer  has  a  ratio  of  4  and  that 
the  push-pull  transformer  has  a  ratio  of  2 
(many  push-pull  transformers  have  a  lower  ratio 
than  this)  between  the  primary  and  one  side  of 
the  secondary,  we  then  obtain  the  following 
figures: 


ARRANGEMENT 


Single  250 
Push-pull  210's 


POWER    IN    LOAD,    PER 

VOLT    SQUARED,    ACROSS 

TRANSFORMER  PRIMARY 

12.8  milliwatts 

12.0  milliwatts 


These  figures  give  a  truer  picture  than  those 
given  previously.  The  difference  between  the  two 
arrangements — a  matter  of  0.8  milliwatts  per 
volt  squared — is  too  small  to  be  appreciable  to 
the  ear  but  at  least  we  may  be  sure  that  an  ampli- 
fier using  a  push-pull  arrangement  wilth  average 
transformer  ratios  and  with  2 10  tubes  won't  give 
any  greater  volume,  with  a  given  input,  than  an 
amplifier  using  a  single  250  tube. 

This  analysis,  summarized  in  the  accompany- 
ing table,  shows  the  250  tube  to  be  about  equal 
to  a  210  push-pull  amplifier  in  most  respects 
excepting  that  of  cost. 

The  complete  characteristics  of  the  250  tube 
are  given  in  the  table  accompanying  this  article 
which  shows  that  this  tube  requires  a  plate  volt- 
age of  about  450  volts  and  takes  a  plate  current 
of  55  mA.  The  power  supply  must  provide  this 
amount  of  current  and  voltage.  The  loud  speaker 
must  be  isolated  from  this  high  plate  current 
by  an  output  device. 

In  some  cases  it  will  be  found  possible  to  sub- 
stitute a  250  type  tube  for  a  210  tube  in  an 
amplifier,  but  frequently  this  will  not  be  possible 
because  the  250  takes  three  times  as  much  plate 
current  as  a  210  and  the  rectifier-filter  system 
may  not  be  able  to  supply  sufficient  voltage  at 
this  higher  current  drain.  The  higher  current 
drain  may  reduce  the  voltage  output  of  the 
power  unit  from  450  volts,  when  3210  type  tube 
is  used,  to  300  volts  or  so  and  it  is  not  worth 
while  to  operate  a  250  at  this  voltage.  Under 
such  conditions  the  tube  cannot  deliver  much 
more  power  output  than  a  210  type  tube, 
operated  at  450  volts. 

ALLOW  ONE  WATT  PER  LOUD  SPEAKER 

"THE  250  type  can  be  used  in  a  properly 
1  designed  push-pull  amplifier  and  such  a  use 
for  the  tube  should  prove  useful  where  sufficient 
power  is  required  for  the  operation  of  several 
loud  speakers  or  for  auditorium  work.  A  push- 


i  CHAR  ACT 

ERISTICS 

OF  THE  TYPE 
RECOMMENDED 

Plate  Voltage 
Negative  Grid  Bias 
Plate  Current 
Plate  Resistance  (a-c) 
Mutual  Conductance 
Voltage  Amplification  Factor 
Max.  Undistorted  Output 

filament 
Max.  Overall 
Base 

MAXIMUM 

250              300 
45                54 
28                35 
2100            2000 
1800            1900 
3.8              3.8 
900            1500 

7.5  Volts 
Height  6}" 
Large  Standard  UX 

350 
63 
45 
1900 
2000 
3.8 
2350 

100 

70 
55 
1800 
2100 
3.8 
3250 

1  .25  Amperes 
Diameter  2}J' 

450 
84 
55 
1800 
2100 
3.8 
4650 

Volts 
Volts 
Milliamp. 
Ohms 
Micromhos 

Milliwatts 

Filter  Choke  Coils 
15  henries  or  more 


To 
Receiver 


GENERAL    CIRCUIT    REQUIREMENTS    FOR    THE    250    TYPE    TUBE 
All  values  are  indicated  except  the  voltage  dividing  resis- 
tances which  vary  according  to  the  receiver  to  be  supplied 


Comparing  the  250  Type  Tube  With  Other  Power  Tubes 

IN  THIS  article  the  new  type  250  power  amplifier  tube  is  compared  with  other  power 
tubes  now  available.  A  summary  of  the  points  developed  more  fully  in  the  article 
follows: 


(a).  The  maximum  power  output  of 
a  type  250  tube  is  4.6  watts,  which  is 
about  three  times  as  much  as  can  be 
obtained  from  a  210  type  tube  and 
about  seven  times  as  much  as  can  be 
obtained  from  a  171  type  tube. 

(b).  The  power  output  of  a  single 
250  is  about  equal  to  the  power  that 
can  be  obtained  from  a  push-pull 
amplifier'using  210  tubes. 

(c).  The  power  supply  equipment 
necessary  for  the  operation  of  the  250 
type  tube  is  about  the  same  as  is  re- 
quired for  the  operation  of  a  push-pull 
amplifier  with  210  type  tubes. 

(</).  Because  ordinary  transformers 
are  generally  cheaper  than  push-pull 
transformers,  it  is  cheaper  to  construct 
a  power  amplifier  with  a  single  250 
type  tube  than  it  is  to  construct  a 
push-pull  amplifier  with  2io's. 

(e).  An  amplifier  using  a  250  will 
give  excellent  quality.  When  the  tube 


is  worked  into  a  load  impedance  equal 
to  twice  the  tube's  plate  impedance, 
rated  output  will  be  delivered  to  the 
load  without  creating  more  than  5 
per  cent,  of  second  harmonic  current. 

(/).  The  volume  output  of  a  single- 
stage  amplifier  using  a  250  will  be 
about  equal  to  that  from  a  push-pull 
amplifier  with  type  210  tubes,  assum- 
ing that  the  input  voltage  is  the  same 
in  each  case  and  that  the  transformer 
feeding  the  2  50  has  a  ratio  of  4  and  the 
input  push-pull  transformer  has  a  ratio 
of  2  (average  figures). 

(/>)•  A  single  250  tube  will  supply  all 
the  power,  with  plenty  in  reserve, 
that  will  be  required  for  the  operation 
of  any  radio  receiver  in  the  home. 
Where  only  moderate  volume  is  re- 
quired, smaller  tubes  such  as  a  171, 
may  be  used  but  where  reserve  power 
is  desired  to  take  care  of  greater 
volume,  the  type  250  may  be  used. 


76 


RADIO  BROADCAST 


JUNE,  1928 


pull  Amplifier  with  250  type  tubes  will  be 
able  to  deliver  to  a  load  about  12  watts  of 
voice  frequency  power — which  is  no  mean 
figure!  A  push-pull  amplifier  using  210  type 
tubes,  outputting  about  four  watts,  can 
be  used  to  supply  about  four  loud  speakers, 
and  a  push-pull  amplifier  with  250  tubes 
will  be  able  to  supply  about  fifteen  loud 
speakers,  assuming  in  both  cases  that  each 
speaker  will  require  about  one  watt  of  energy. 
In  a  home  installation  a  single  250  tube 
should  give  all  the  power  that  will  ever  be 
required,  with  plenty  in  reserve. 

Several  manufacturers  have  already  an- 
nounced apparatus  suitable  for  use  with  the 
250  type  tube.  The  General  Radio  Com- 
pany has  designed  a  complete  line  of 
transformers,  filter  units,  and  output  de- 
vices for  use  with  the  250  tube  and  a 
description  of  this  apparatus  will  be  found 
in  the  New  Apparatus  section  of  this  issue. 

The  Silver-Marshall  Company  has  de- 
signed two  amplifiers  for  the  use  of  the  250 
tube;  one  a  single-stage  affair,  and  the  other 
a  complete  two-stage  amplifier.  The  two- 
stage  amplifier  is  illustrated  herewith.  It 
uses  a  type  226  tube  in  the  first  stage  and 
a  250  in  the  second  stage.  Plate  supply  is 


LEFAX  RADIO  HANDBOOK — (Seventh  Loose- 
Leaf  Edition).  Published  by  Lefax,  Inc. 
Philadelphia,  Pennsylvania.  Subscription, 
$5.00  a  year. 

IS  Lefax  Handbook  is  in  the  familiar 
form  of  a  loose-leaf  notebook  about  seven 
by  five  inches.  The  first  chapter,  "What 
Radio  Does,"  is  largely  a  summary  of  the  various 
uses  of  radio  communication,  from  the  distribu- 
tion of  time  signals  to  television,  with  some  dis- 
cussion of  special  devices  like  chain  broadcasting. 
Next,  under  "  Fundamental  Principles  of  Radio" 
the  behavior  of  direct  and  alternating  currents, 
waves,  and  modulation  methods  is  described. 
The  following  chapters  are  on  "  Elements  of 
Receiving  and  Transmitting  Apparatus,"  "As- 
sembly of  Receiving  Sets,"  "Operation  of  Re- 
ceiving Sets  and  Their  Accessories,"  "Antennas." 
The  next-to-the-last  section  contains  conversion 
tables,  definitions  of  radio  terms,  codes,  formulas, 
tube  characteristics,  etc.  A  complete  index  is 
supplied.  The  material  is  gleaned  from  such 
journals  as  the  Proceedings  of  the  Institute  of 
Radio  Engineers,  the  Bell  System  Technical 
Journal,  Bureau  of  Standards  publications, 
RADIO  BROADCAST,  manufacturers'  bulletins,  etc. 
It  is  clearly  abstracted  and  an  extensive  survey 
of  practical  radio  engineering  material  is  crowded 
into  this  loose-leaf  book.  The  editor  is  Dr.  J.  H. 
Dellinger,  Chief  of  the  Radio  Laboratory  of  the 
Bureau  of  Standards.  The  system  is  based  on  the 
issuance  of  sixteen  sheets  a  month,  ready  to  be 
inserted  in  the  binder.  Obviously  the  rate  of 
progress  of  radio  technology  is  such  as  to  require 
some  such  scheme  as  a  supplement  to  scientific 
textbooks  which  can  appear  only  in  widely 
separated  editions. 

RADIO  ENGINEERING  PRINCIPLES,  by  Henri 
Lauer  and  Harry  L.  Brown.  Second  Edition, 
January,  1928.  McGraw-Hill  Book  Co., 
Inc.  301  pages.  $3.50. 

THIS    text,    first    issued     in     1919,     follows 
Morecroft   into    a    second    edition.    Unfor- 
tunately   the   death    of   one    of    the    authors, 
Harry  L.  Brown,  occurred  just  before  the  volume 
appeared.  With  Mr.  Lauer,  he  was  able  to  com- 


IKPUT      1.5U.AC.  2.25U.AC. 

1      t       >       I       i 


+135  +90+45   B-   SPEAKER 

' 


Boole  Reviews 

plete  a  creditable  piece  of  work  before  he  died. 
The  book  is  less  extensive  than  Morecroft's,  but 
it  is  excellent  for  those  whose  requirements  are 
satisfied  with  a  shorter  and  less  expensive  text. 
The  treatment  is  based  on  the  electron  concep- 
tion of  matter,  with  only  moderate  resort  to 
mathematics  and  no  recourse  to  mechanical 
analogies,  with  which,  frequently,  the  student  is 
even  less  familiar  than  with  the  radio  theory  he 
wants  to  learn.  The  book,  as  the  title  indicates, 
is  concerned  with  principles  rather  than  with 
concrete  apparatus.  It  begins  with  a  considera- 
tion of  the  underlying  electrical  theory,  the 
properties  of  oscillatory  circuits,  antenna  sys- 
tems and  radiation,  proceeds  to  a  description 
of  damped  and  continuous  wave  telegraphy, 
devotes  four  long  chapters  to  vacuum-tube 
theory,  and  ends  with  chapters  on  radio  tele- 
phony and  miscellaneous  applications  of  radio 
The  principal  additions  to  the  first  edition 
are  in  the  chapters  on  three-electrode  tubes. 
Numerous  special  topics,  such  as  aircraft  radio 
compass  work,  the  mathematical  theory  of  the 
push-pull  amplifier  and  frequency  doubler,  the 
theory  of  the  balanced  modulator,  piezo-electric 
resonators  and  oscillators,  are  adequately  treated. 
The  book  is  a  very  scholarly' presentation.  Pages 
69-73  contain  one  of  the  few  adequate  descrip- 
tions of  the  wave  antenna  to  be  found  in  radio 
texts.  The  references  to  little  known  articles, 
especially  foreign  sources,  are  alone  sufficient 
to  warrant  inclusion  of  the  second  edition  in 
every  radio  engineer's  library. 

A  POPULAR  GUIDE  To  RADIO,  by  B.  Francis 
Dashiell,  The  Williams  and  Wilkins  Company, 
Baltimore,  289  pages,  $3.50. 

THIS  book  is  written  for  the  non-technical 
reader,  according  to  the  publishers.  The 
author  is  only  incidentally  a  radio  man;  his  reg- 
ular employment  is  in  the  Weather  Bureau  at 
Washington.  The  job  of  presenting  the  principles 
and  mechanism  of  radio  appears  to  this  reviewer, 
who  is  a  professional  radio  man  and  technically 
inclined,  to  have  been  competently  done.  Ap- 
parently Mr.  Dashiell  knows  quite  as  much 
about  the  art  as  if  he  had  lived  in  it  all  his  life. 
But  it  is  not  clear,  and  this  book  does  not  make 


obtained  from  a  rectifier-filter  system  using 
two  type  281  tubes  in  a  full-wave  circuit. 
A  glow  tube  is  used.  The  single-stage  am- 
plifier is  similar  to  the  two-stage  unit  that 
is  illustrated  except  that  the  apparatus  for 
the  first  stage  is  omitted.  This  latter  am- 
plifier may  well  be  used  to  replace  an 
unsatisfactory  last-stage  amplifier  in  any 
radio  receiver.  From  both  of  these  ampli- 
fiers can  be  obtained  the  necessary  B  volt- 
ages for  the  operation  of  the  other  tubes  in 
the  receiver  proper,  and  in  addition  the 
two-stage  amplifier  will  also  supply  a.  c. 
voltages  for  the  filaments  of  any  a.  c.  tubes 
that  may  be  used  in  the  set.  The  two-stage 
amplifier  is  also  especially  satisfactory  for  use 
with  a  phonograph  pick-up  to  play  phono- 
graph records.  Both  of  these  amplifiers  can  be 
home  constructed  with  little  trouble,  from 
data  obtainable  from  Silver-Marshall  through 
RADIO  BROADCAST. 


A  COMPLETE  A.C.  AMPLIFIER 

This  commercially  available  unit 
employs  one  cx-35o  as  the  power 
tube.  The  second  and  third  sets  of 
binding  posts  at  the  top,  reading 
from  the  left  supply  a.c.  filament 
voltages  for  the  set.  This  unit  is 
from  Silver-Marshall 


it  clearer,  just  how  a  technical  subject  can  be 
expounded  to  a  non-technical  audience.  In  so 
far  as  A  Popular  Guide  to  Radio  elucidates  and 
instructs,  it  is  moderately  but  quite  definitely 
technical.  It  is  not  made  less  technical  by  the 
insertion  of  a  frontpiece  showing  Carlin  and 
McNamee  broadcasting  a  football  game.  If 
"non-technical"  means  free  from  mathematics, 
then  the  book  is  non-technical,  true  enough. 
But  this  merely  results  in  passages  like  the  fol- 
lowing description  of  "Impedance  in  an  Alter- 
nating Current  Circuit":  "A  circuit  may  have 
inductance  and  capacity  in  addition  to  its 
natural  electrical  resistance  when  an  alternat- 
ing current  is  flowing.  When  this  combined  re- 
actance and  natural  resistance  operates  to  ob- 
struct the  flow  of  an  alternating  current  it  is 
known  as  the  impedance.  However,  as  inductive 
and  capacitive  reactances  are  the  reverse  of  each 
other,  the  total  reactance  of  a  circuit  is  the  dif- 
ference between  the  two  reactances  measured  in 
ohms  and  giving  the  impedance  designation  to 
the  predominating  reactance.  The  electrical  re- 
sistance in  ohms  cannot  be  added  to  this  total 
reactance  to  obtain  the  impedance.  Graphically, 
they  should  be  combined  as  straight  lines  in  pro- 
portionate lengths.  Assuming  them  as  two 
forces  acting  together  at  right  angles,  their 
resultant  is  the  impedance."  This  sort  of  writing 
is  neither  wholly  accurate,  readily  comprehen- 
sible, nor  compact.  Its  somewhat  puffy  and  la- 
bored quality  arises  from  the  fact  that  it  is  the 
wrong  way  of  doing  the  thing.  And  incidentally 
impedance  is  just  as  natural  as  resistance. 

When  Mr.  Dashiell  does  not  attempt  the  im- 
possible he  turns  out  a  creditable  piece  of  work. 

There  is  a  lot  of  sound,  up-to-date  informa- 
tion, with  a  few  platitudes  intermingled,  and 
here  and  there  a  debatable  statement,  such  as 
that  on  page  170  about  the  neutrodyne  circuit. 
where  the  names  of  Hogan.  Hazeltine,  and  At- 
water  Kent  are  mentioned,  and  not  a  word  about 
Rice  and  Alexanderson.  The  photographs  are 
well-chosen  and  the  figures  nicely  drawn.  After 
reading  it  one  is  left  with  the  impression  that 
this  is  a  worthy  book,  but  exactly  for  whom  was 
it  written? 

— CARL  DREHER. 


RADIO  BROADCAST  Photograph 


By  W.  H.  WENSTROM 

Lieut.,  Signal  Carpi,  U.  S.  A. 


IOME  of  the  most  fascinating  fields  of  radio 
lie  outside  that  narrow  band  in  which  the 
broadcasting  stations  do  battle.  Voice  and 
music  from  Europe,  code  from  tossing  ships  or 
lonely  airplanes,  faint  signals  from  amateurs  at 
the  antipodes  or  explorers  in  arctic  cold  and 
equatorial  heat — all  these  are  echoing  along  the 
lanes  of  the  ether.  To  hear  them  we  must  have  a 
receiver  that  is  simple,  reliable,  accessible,  effi- 
cient and  flexible.  As  the  Navy  recently  applied 
the  name  "Cornet"  to  an  unusually  flexible 
transmitter,  so  this  receiver,  able  to  shift  rapidly 
from  one  frequency  to  another — to  play  a  vari- 
ety of  tunes — is  also  called  "Cornet." 

The  general  design  is  apparent  from  the  circuit 
diagram,  Fig.  I,  and  the  photographs.  For  sim- 
plicity we  go  back  to  that  venerable  amateur 
mainstay,  a  capacitatively  controlled  regenera- 
tive detector  with  one  stage  of  audio;  and  we 
avoid  tuned  radio-frequency  and  screen-grid  tube 
arrangements.  On  the  front  panel  are  one  main 
and  two  auxilliary  controls,  while  two  adjusting 
controls  are  on  the  sub-panel. 

Reliability  is  secured  by  using  the  best  parts 
that  we  can  buy.  We  avoid  the  pitfalls  of  some 
poorly  made  pig-tail  condensers,  noisy  grid  leaks 
and  the  like.  Each  radio  part  must  meet  two 
exacting  standards — the  electrical  and  the 
mechanical. 

Accessibility  is  often  neglected  in  radio  design. 
The  best  set  in  the  world  will  occasionally  develop 
trouble,  which  must  be  located  and  remedied  at 
once.  This  set  is  accessible  because  of  sub-panel 
construction  and  general  openness  of  design. 

In  pure  efficiency,  the  regenerative  detector 
has  never  yet  been  equalled.  Unusual  features  of 
this  set  include  a  micro-vernier  condenser  of 
about  3.o-mmfd.  maximum  capacity  and  a  grid 
biasing  potentiometer  which  controls  the  sensi- 
tiveness, selectivity  and  oscillating  characteris- 
tics of  the  detector  tube.  All  three  tuning  con- 
densers are  mounted  directly  against  a  panel 
backed  with  aluminum  which  in  turn  is  connected 
through  the  sub-panel  brackets  to  ground;  so 
that  body  capacity,  as  found  in  the  usual  short- 
wave receiver,  simply  does  not  exist. 

Above  all,  the  receiver  is  flexible.  The  Silver- 
Marshall  plug-in  coil  system  is  used  on  account 
of  its  electrical  efficiency,  convenience,  and  com- 
pactness. The  set  is  primarily  designed  to  cover, 
with  four  coils,  the  range  from  14  to  200  meters. 
This  range  is  obtained  by  using  a  tuning  con- 
denser somewhat  larger  than  usually  recom- 
mended by  Silver-Marshal.  Additional  bands 
can  be  covered,  as  desired,  by  extra  coils. 


CONSTRUCTIONAL    DETAILS 

HpHE  arrangement  of  parts  is  shown  in  the 
1  photographs.  First,  drill  the  metal  and  insu- 
lating front  panels;  then  assemble  the  front 
panels,  the  sub-panel  brackets,  and  the  sub- 
panel.  All  are  bolted  together  with  small  nick- 
eled machine  screws.  For  best  appearance,  the 
front  panel  should  slope  back  about  15  degrees 
from  the  vertical. 

Three  Cardwell  condensers,  with  their  asso- 
ciated General  Radio  dials,  are  mounted  on  the 
front  panels.  The  right  condenser,  viewed  from 
front  panel,  is  of  o.ooo25-mfd.  maximum  capac- 
ity, and  may  be  either  the  old,  flat-plate  type, 
which  sells  very  cheaply  in  many  stores,  or  the 
new  taper-plate  type.  The  left  condenser  should 
have  a  maximum  capacity  of  about  0.000165 
mfd.  This  is  obtained  from  an  old  type  0.00025 
by  removing  two  rotor  and  two  stator  plates, 
leaving  four  rotors  and  three  stators.  If  the  old 
type  0.00025  cannot  be  secured,  the  new  taper- 
plate  0.00015  may  t>e  used,  though  with  this 
latter  condenser,  minute  uncovered  frequency 
bands  will  appear  between  the  coil  ranges.  Of 
course,  the  coils  may  be  slightly  redesigned  to 
cover  these  breaks;  or  the  standard  S-M  coils 


(.  r  HE  set  described  here  by  Lieut.  Wenslrom  has 
•*•  two  features  unusual  in  receivers  designed  to 
cover  the  high  frequencies:  (a),  a  potentiometer 
across  the  A  battery  to  adjust  the  bias  voltage  on 
the  gird  of  the  detector  so  that  the  best  operating 
point  may  he  found;  and  (b),  a  small  vernier  con- 
denser across  the  main  tuning  condenser  to  enable 
the  operator  to  tune  very  closely  to  a  given  fre- 
quency, or  to  follow  a  fading  signal  with  greater 
ease.  On  lest  in  the  Laboratory,  this  receiver  worked 
very  well,  5  sw  at  Chelmsford,  England,  being  heard 
at  6  p.  m.  E.  S.  T.,  without  difficulty.  The  biasing 
potentiometer  adds  much  to  the  sensitivity  of  this 
set.  It  is  common  amateur  practice  to  use  a  high- 
ratio  transformer,  working  out  of  the  detector  into 
the  first  audio  tube.  Lieut.  Wenstrom  has  used  a 
low  ratio  transformer  which  provides  better  repro- 
duction when  the  set  is  used  for  receiving  short- 
wave broadcast  transmissions.  A  vernier  dial  with 
a  greater  reduction  ratio  than  the  one  employed — 
such  as  the  Karas — might  make  tuning  somewhat 
easier,  perhaps  even  obviating  the  necessity  for  the 
auxiliary  tuning  condenser. 

— THE  EDITOR. 


77 


may  be  used,  with  some  loss  of  tuning  range. 
The  center  condenser  is  a  Cardwell  "Balancet" 
of  the  smallest  size,  with  all  plates  removed  ex- 
cept the  back  stator  and  the  front  rotor.  The 
"phones"  jack  is  placed  at  the  lower  right  corner 
of  the  front  panel,  insulated  from  the  metal 
by  a  bushing  of  bakelite,  hard  rubber  or  fibre. 
Because  the  set  must  often  be  switched  on  and 
off  without  jarring  it  or  disturbing  the  wave- 
length setting,  an  external  knife  switch  is  used 
by  the  writer  rather  than  a  filament  switch  on 
the  panel. 

On  the  upper  side  of  the  sub-panel  are  mounted 
the  coil  socket,  the  two  tube  sockets,  two  fila- 
ment ballasts,  two  grid  leaks  and  knobs  for  the 
antenna  condenser  and  the  potentiometer.  On 
its  lower  side  are  the  potentiometer,  the  audio 
transformer,  the  r.f.  choke,  the  grid  condenser, 
and  the  antenna  coupling  condenser,  for  which 
a  Silver-Marshall  midget  is  chosen  because  of  its 
low  minimum  capacity.  The  binding  posts  are  set 
into  the  back  edge  of  the  sub-panel.  The  ampli- 
fier grid  leak  is  clipped  in  when  wanted  for  phone 
work;  the  glass  casing  of  the  detector  grid  leak 
should  be  washed  free  of  paper  and  glue. 

Wiring  is  best  done  in  definite  steps.  The  fila- 
ment circuit  is  first  wired  and  tested.  Then  come 
the  other  circuits  in  natural  order:  antenna- 
ground,  detector  grid,  detector  plate,  amplifier 
grid,  and  amplifier  plate.  Grid  leads,  of  course, 
are  reasonably  short,  and  all  leads  are  fairly 
straight  without  sharp  angles.  Though  No.  14 
wire  is  used  in  places  for  rigidity,  most  of  the 
wiring  is  done  with  solid,  rubber  covered  wire 
of  about  No.  20  size,  known  in  telephone  par- 
lance as  "pothead"  wire.  It  is  plainly  absurd  to 
insist  on  large  wire  leads  in  series  with  coils,  high 
resistances  and  the  like.  Acme  Celatsite  is  also 
quite  satisfactory  and  convenient. 

The  four  plug-in  coils  are  those  supplied  in  the 
Silver-Marshall  No.  1 17  short-wave  set,  rewound 
with  No.  26  enameled  copper  wire  except  as 
otherwise  indicated.  They  are  completely  de- 
scribed in  the  coil  table.  Three  optional  extra 
coils  are  also  listed. 

The  detector  tube  is  preferably  a  Ceco  type 
"  H ,"  though  it  may  be  any  good  make  of  high-mu 
tube,  or  even  one  of  the  2OI-A  type.  [The  2OI-A 
is  satisfactory  as  a  detector  in  this  circuit,  of 
course.  If  the  Ceco  type  H,  or  other  special 
detector  tubes,  or  even  a  standard  high-mu  tube 
is  used,  the  "gain"  will  increase.  However,  in  the 
latter  case,  quality  may  be  impaired  to  some 
extent  when  this  set  is  used  for  headphone  recep- 
tion.— Editor.]  The  amplifier  tube  is  a  2OI-A. 


78 


RADIO  BROADCAST 


JUNE,  1928 


COIL  TABLE 

COILS  for 

the  first  four 

bands  listed  below  are  those 

upplied  in  the  Silver-Marshall  No.  117  short-wave 

coil  set, 

rewound  with 

No.  26  enameled  copper  wire 

,  except  as  otherwise 

indicated  in  the  last  column. 

BAND 

COIL  RANGE 

GRID  TURNS 

TICKLER  TURNS 

REMARKS 

20m. 

14-28  m. 

3 

3 

No.  24  wire,  with  triple  (the 

standard  S-M)  spacing 

40m. 

26-52  m. 

6 

5 

Grid  1  less;  tickler  2  less  than 

S-M  standard 

80  m. 

51-110  m. 

15 

8 

Grid  3  more;  tickler  2  less. 

160m. 

100-200  m. 

36 

16 

Grid,  10  more;  tickler  same. 

Shortest  wave 

1O-21  m. 

2 

3 

No.  24  wire;  quadruple  spac- 

ing. 

Ship  waves 

550-1100  m. 

Standard  S-M  No.  111-D 

Long  wave 

1100-2000  m. 

approx.                  Standard  S-M  No.  111-E 

No  cabinet  is  included  in  the  plans,  as  a  small 
writing  desk  serves  the  purpose,  and  the  builder 
may  have  his  own  especial  preferences  anyhow. 

OPERATION 

TO  place  the  set  in  operation,  connect  the 
6-volt  filament  leads,  see  that  the  tubes  light, 
and  then  connect  the  4j-volt  B  battery.  Next, 


CALIBRATION  CURVE 
40  METER  COIL 


50 


35 


25 


0       10      20      30      40       50      60       70      80      90     10Q 
DIAL  SETTING 

FIG.    2 

Calibration  curve  of  the  4o-meter  coil  and  con- 
denser combination  used  in  this  set.  Slight  electri- 
cal differences  in  parts  used  by  constructors  may 
make  their  calibration  different  from  this 


place  one  of  the  coils,  say  the  4O-meter  one,  in 
the  coil  socket.  With  the  left-hand  condenser  set 
at  any  reading,  increasing  the  right-hand  con- 
denser should  put  the  set  into  oscillation  with  a 
weakly  audible  "plop."  The  potentiometer  is 
adjusted  to  minimize  this  "plop"  so  that  the  set 


goes  smoothly  into  and  out  of  oscillation.  In 
general,  the  potentiometer  arm  is  turned  toward 
the  positive  side  of  the  circuit  for  phone  work  and 
slightly  toward  the  negative  side  for  code  re- 
ception. As  the  left  dial  is  moved  to  a  higher 
reading,  a  correspondingly  higher  reading  on 
the  right  dial  will  usually  be  necessary  to  produce 
oscillation.  If  the  r.f.  choke  is  doing  its  work, 
there  should  be  no  "dead  spots"  in  the  tuning 
range.  At  any  wavelength  setting  of  the  left 
dial,  the  most  sensitive  right  dial  setting  for 
phone  is  just  below  or  at  the  oscillating  point; 
for  code,  just  above  it. 

With  these  preliminary  tests  completed,  the 
set  is  connected  to  the  ground  and  to  the  antenna, 
a  single  wire  anywhere  from  20  up  to  750  feet  in 
length.  [A  small  indoor  antenna  with  this  set  in 
most  locations  will  probably  serve  very  well 
for  all  purposes.. — Editor.]  The  4O-meter  coil 
being  in  place,  signals  should  be  heard  as  the 
left  dial  is  moved  over  its  entire  range,  for  this 
band  is  busy  at  any  hour  of  the  day  or  night. 
If  any  "dead  spots"  now  occur,  blame  them  on 
the  antenna,  and  decrease  the  antenna  coupling 
condenser  to  the  point  where  they  are  not  trou- 
blesome. This  antenna  condenser  is  always  set 
at  the  maximum  capacity  which  will  not  interfere 
with  the  convenient  operation  of  the  oscillation 
control.  After  a  signal  has  been  tuned-in  wilh 
the  left  dial  and  brought  to  full  strength  with 
the  right  one,  apply  the  finishing  refinement  of 
tuning  with  the  center  dial  and  its  diminutive 
condenser.  This  control  is  so  fine  that  a  single 
beat  note  spreads  over  5  to  10  degrees,  and  the 
"zero  beat"  for  phone  reception  is  easily  pro- 
duced. 


CALIBRATION 

FOR  maximum  usefulness  all  coils  should  be 
carefully  calibrated.  The  data,  including  the 
settings  of  the  left  dial  for  various  wavelengths, 
may  be  plotted  as  a  graph,  which  is  scientific 
and  thorough  (see  Fig.  2);  or  they  may  be  listed 
in  a  table,  which  is  more  convenient  to  read. 
Such  a  table  for  the  4O-meter  coil  employed  by 
the  writer  is:  o-26m.,  i^-^om.,  ^6-^-j.^m.,  45- 
4Om.,  5Q-43m.,  ioo-$2m.  While  this  table  is 
approximately  correct  for  the  set  here  pictured, 
changes  in  detector  tube,  wiring  and  variations 
in  coils  used  by  those  who  duplicate  this  set,  or 
other  circuit  constants  would  make  it  practically 
useless  for  another.  Each  set  must  be  calibrated 
individually. 

First,  a  wavemeter  must  be  bought,  borrowed 
or  made.  Then,  the  left  receiver  dial  is  set  at 
some  convenient  reading  (say  O),  the  antenna 
condenser  is  set  to  minimum,  the  vernier  to  50, 
and  the  right  dial  to  two  points  above  oscillation. 
Place  the  wavemeter  coil  in  what  would  be  a 


FIG.     I 
Circuit  diagram  of  Lieut.  Wenstrom's  receiver 


FIG.    3 

General   instructions  on   altering  the  coil  form 

for  the  20-,  40-,  80-,  160-  and  lo-meter  bands. 

(See  the  coil  table  on  this  page) 

prolongation  of  the  set  coil,  and  rotate  the  wave- 
meter  dial  slowly.  Two  "plops"  are  heard,  one 
as  the  set  goes  out  of  oscillation  and  another 
as  it  goes  back  into  it.  Now  move  the  wave- 
meter  a  little  farther  away,  and  repeat  the  per- 
formance until  the  two  "plops"  are  practically 
one.  Or  note  the  point  midway  between  the  two 
"  plops."  This  point  on  the  wavemeter  scale  is  the 
wavelength  to  which  the  receiver  is  tuned.  The 
left  dial  is  now  moved  to  a  new  setting  and  every- 
thing is  repeated.  All  the  coils  are  calibrated  in 
the  same  way.  If  you  wish  to  find  the  receiver 
dial  reading  for  any  particular  wavelength,  set  it 
on  the  wavemeter  and  rotate  the  receiver  dial. 

A  wavemeter  is  simple  enough  to  make.  The 
basic  circuit  consists  essentially  in  a  coil  and  a 
variable  condenser.  The  homemade  product  must 
be  calibrated  from  a  standard  one.  By  checking 
both  against  the  receiver,  data  is  secured  for 
a  homemade  wavemeter  curve  similar  to  the 
curve  of  Fig.  2.  Of  course  it  is  possible  to  cali- 
brate one's  receiver  by  picking  up  signals  from 
well-known  stations.  For  example  the  amateur 
4O-meter  band  is  bounded  by  NAA  at  about  37.4 
meters  at  one  end  and  by  wiz  at  43  meters  at 
the  other.  Standard  frequency  signals  are  sent 
out  at  regular  intervals  by  wwv,  the  Bureau  of 
Standards  station,  (see  page  84)  and  others. 

WHERE   TO    FIND   THE   STATIONS 

WE  NEED  have  no  illusions  about  the  qual- 
ity of  short-wave  broadcasting,  nor  any 
fear  that  it  will  replace  the  present  system  of 
allocation  of  stations  in  the  1500-550-^.  band. 
Fading  is  usually  quite  severe,  and  the  signal 
strength  of  distant  stations  varies  widely  from 
day  to  day.  In  America,  WGY  on  21.9  and  32.77 
meters  and  KDKA  on  25  and  62  meters  transmit 


JUNE,  1928 


THE  "CORNET"  MULTIWAVE  RECEIVER 


79 


THE    CORNET    MULTIWAVE 


RADIO  BROADCAST  Photograph 
RECEIVER 


the  regular  programs  of  their  standard-wave 
broadcast  plants.  Their  signals  have  world-wide 
range,  and  quality  dependent  on  the  atmospheric 
and  Heaviside  layer  conditions.  In  England, 
5  sw  at  Chelmsford  carries  the  regular  London 
programs  on  24  meters,  and  is  heard  any  weekday 
afternoon  up  to  7:00  p.  m.  E.  S.  T.  Reception  of 
this  station  is  really  good  perhaps  one  or  two 
days  a  week.  The  signal  of  PCJJ  at  Eindhoven, 
Holland,  is  weaker  and  more  variable  than  that 
of  5  sw.  It  comes  through  at  present  late  Tues- 
day, Thursday,  and  Saturday  afternoons  (East- 
ern time).  So  far,  these  two  have  been  the  only 
foreigners  regularly  heard,  and  their  programs 
have  appealed  chiefly  by  their  novelty.  Perhaps 
within  a  few  years  most  important  nations  will 
have  high  power,  short-wave  telephone  trans- 
mitters, and  fading  will  be  minimized  by  sepa- 
rated, synchronized  transmitters  or  some  such 
scheme.  Then  international  broadcasting  will 
truly  begin,  and  this  receiver  will  be  able  to 
choose  its  programs  between  five  continents. 

For  one  who  reads  code  the  pleasures  of  this 
receiver,  and  of  all  radio,  are  greatly  extended. 
NAA  at  Washington,  on  approximately  24.9,  37.4 
and  74.8  meters,  broadcasts  weather  at  8. 15  and 
10:30  a.  m.  and  p.  m.;  time  at  12:00  noon  and 
10:00  p.  m.;  and  press  at  1.30  a.  m.,  E.  S.  T. 
Station  NPG  at  San  Francisco,  on  36  and  72 
meters,  sends  weather  at  6:15  and  7:30  a.  m. 
and  p.  m.,  P.  S.  T.  To  keep  up  to  date  on  these 
schedules,  one  must  consult  the  weekly  radio 
sections  of  large  newspapers.  [A  list  of  Navy 
transmissions  appeared  in  this  magazine  for 
May,  1928. — Editor.]  The  biggest  nuisance  in 
the  short-wave  spectrum  is  the  harmonics  of 
long  wave  broadcasting  stations,  which  delude 
the  listener  in  this  short-wave  section  of  the  band 
into  thinking  he  hears  something  new. 

Many  important  exploring  expeditions  trans- 
mit code.  Most  of  them  favor  the  waves  around 
30  meters.  This  summer  there  will  be  at  least 
one  expedition  near  the  North  Pole,  one  near  the 
South  Pole,  plenty  of  transocean  flights,  and 
at  least  one  round-the-world  dirigible  flight. 
Some  far  distant  amateurs  come  in  from 
18  to  24  meters  during  many  of  the  daylight 
hours,  though  most  of  these  experimenters  use 
the  4O-meter  band.  In  this  region,  Europeans 
between  43  and  47  meters,  just  above  the  United 
States  band,  begin  to  be  heard  about  an  hour  or 
two  before  sunset.  Before  sunrise  signals  from 
the  Australians  and  New  Zealanders  come 
through  around  33  meters.  There  are  some 


United  States  amateur  telephone  stations  be- 
tween 84  and  85  meters. 

Six  hundred  meters  is  the  international  marine 
calling  wave.  Rapid  dots  and  dashes  from  ship 
sparks  are  always  audible  near  the  seacoast.  On 
this  wave,  too,  sounds  at  times  the  staccato 
sos  for  which  broadcasting  stations  shut  down. 
Copying  signals  from  a  ship  in  distress  and  the 
vessels  going  to  her  assistance  is  the  most  exciting 
thing  in  radio.  Of  course  it  is  in  no  sense  a  pleas- 
ure; the  lesson  of  Robert  Louis  Stevenson's 
Merry  Men  is  plain.  For  actual  message  handl- 
ing, ships  use  waves  around  700  and  900  meters. 
On  looo  meters  in  foggy  weather,  the  coastal 
radio  beacons  flash  their  distinctive  groups. 
Radio  compass  bearings  are  given  on  800  meters. 
For  data  on  the  coils  which  cover  all  the  bands 
discussed  in  this  article,  see  the  table  on  page  78. 

This  "Cornet"  multiwave  set  opens  the  door 
to  reception  interesting  and  unlimited,  or  limited 


only  by  the  skill  and  patience  of  the  operator. 
And  what  more  could  he  ask? 

THE    PARTS   WHICH   WERE    USED 

THE  following  list  of  parts  gives  the  apparatus 
used  in  the  writer's  receiver.  Naturally,  other 
parts,  electrically  and  mechanically  similar  may 
be  used.  Coils  and  condensers  mentioned  here 
are  of  well-known  manufacture  and  have  been 
altered  in  ways  indicated  in  the  text. 

Ci     Cardwell   type    141-6   25O-mmfd.   variable 
condenser,  (revised  as  indicated  in  the  text) 
Cj     Cardwell  Balance!  j-mmfd.  (approx.)  vari- 
able condenser 

C3     Sangamo  i5O-mmfd.  fixed  condenser 
Ci     Cardwell   type    141-6   25O-mmfd.   variable 

condenser 

Ci     Silver-Marshall  type  340  midget  condenser 
LI,  LI     Coils  wound  on  Silver-Marshall  forms 

(as  described  in  text) 

Ls     Silver-Marshall  Type  275  R.F.  choke 
Ri     Tobe  Tipon  6-megohm  grid  leak 
R-i    General  Radio  type  301,  zoo-ohm  potenti- 
ometer 
R3     Daven    J-ampere    filament    ballasts    with 

mountings 

Ri    Tobe  Tipon  0.5   megohm   resistance   (op- 
tional, see  text) 

Ti     Thordarson   small    type   2:1    audio   trans- 
former 

I        Silver-Marshall  coil  socket  type  515 
I        Benjamin  navy  spring  type  socket 

1  Hoosick  Falls  navy  plain  type  socket 

2  Grid  leak  mountings 

2  Knobs,  Kurz-Kasch,  ij-inch 

i    •    General  Radio  type  303  4-inch  vernier  dial 

I  General  Radio  type  317  4-inch  plain  dial 

I  General  Radio  type  310  Zj-inch  plain  dial 

5  Eby  plain  binding  posts 

i  Pacent  open  circuit  jack 

i  Insulating  bushing  for  jack 

i  panel  7"  x  14",  hard  rubber  or  bakelite 

i  back  panel,  7"  x  14",  aluminum 

1  Sub-panel,  4"  x  14",  hard  rubber  or  bakelite 

2  Benjamin  adjustable  sub-panel  brackets 


RADIO  BROADCAST  Photograph 

HOW   THE    MULTIWAVE    SET   LOOKS    FROM   THE   TOP 
Four  of  the  coils  used  are  shown  with  their  convenient  adhesive  tape  labels 


AN 

OF   WIDE    USE    TO 
EVERT  RADIO  EX- 
PERIMENTER 

With  an  inexpensive  milliam- 
meter arranged  as  described  in 
this  article,  a  portable  and 
very  useful  measuring  set  can 
be  made.  The  set  will  measure 
practically  all  of  the  common 
d.c.  voltages  and  currents  up 
to  5  amperes  and  1000  volts. 
It  is  especially  useful  in  test- 
ing B  power  units.  The  crystal 
detector  circuit  malfes  this  unit 
useful  as  an  r.f.  resonance  in- 
dicator in  transmitter  circuits 


From  Milliammeter  to  Multimeter 


lERHAPS  one  of  the  fundamental  reasons 
why  electrical  science  has  grown  so  tre- 
mendously in  its  comparatively  short  life 
span  is  the  ease  and  accuracy  with  which  elec- 
trical measurements  can  be  made.  An  ability 
to  determine  accurately  the  magnitudes  and  re- 
lations of  the  quantities  involved  in  any  work 
naturally  leads  to  intelligent  interpretation  and 
utilization  of  those  quantities.  Applying  the  last 
statement  to  the  radio  worker,  an  ability  to  meas- 
ure the  B-battery  voltage  at  17  volts  per  22-volt 
block  is  much  more  conducive  to  results  than 
wondering  if  low  B  batteries  are  spoiling  the  re- 
ception; and  plugging-in  to  measure  the  plate 
current  of  a  tube  can  be  made  to  save  many 
minutes,  if  that  particular  tube  has  gone  dead. 

It  is  surprisingly  simple  to  take  a  low-range 
milliammeter  and  make  an  almost  universal 
measuring  instrument  of  it.  The  instrument  can 
be  made  to  measure  the  whole  gamut  of  d.c.  radio 
voltages,  from  the  voltage  of  a  dry  cell  on  up 
through  the  various  A,  B,  and  C  voltages  to 
those  used  for  plate  supply  in  transmission  work. 
Starting  with  a  meter  of  one  milliampere  full- 
scale  deflection,  the  current  range  can  be  run  up 
as  high  as  desired ;  and  then  the  meter  can  be  used 
for  indicating  a  few  other  quantities  on  the  side. 
The  extension  of  the  milliammeter  range  to  read 
both  voltages  and  currents  of  various  magnitudes 
is  accomplished  by  means  of  what  are  known  as 
multipliers  and  shunts. 

Suppose  two  resistors  are  put  in  parallel  in  a 
circuit;  the  current  will  naturally  divide,  part 
going  through  one  resistor  and  the  rest  through 
the  other.  An  idea  as  to  how  the  current  divides 


G.  F.  Lampkin 

through  the  two  paths  can  be  had  if  the  values 
of  the  two  resistors,  RI  and  R2,  are  known.  The 
current,  Iz,  in  resistor  R2  is  equal  to: 

Ri 


RJ 


X  TOTAL  CURRENT 


And  similarly,  the  portion  li  in  the  path  RI  is 
equal  to: 


Ri 


x  TOTAL  CLRRENT 


The  idea  of  the  shunt  is  to  bypass  a  part  of  the 
total  current  around  the  milliammeter,  and  let 
only  enough  current  go  through  the  latter  to  give 
full-scale  deflection  when  the  total  current  to  be 
measured  is  flowing.  If  the  total  current  is  less 
than  that  required  to  give  full-scale  deflection, 
with  a  given  shunt,  the  meter  reading  will  be  less 
in  the  same  proportion.  By  properly  choosing  the 
resistance  of  the  shunt,  the  meter  can  be  used  to 
read  any  magnitude  of  total  current.  If  the  shunt 
resistance  is  very  low,  the  meter  can  be  used  to 
read  large  total  currents;  or,  conversely,  if  the 
shunt  resistance  is  high,  small  currents  can  be 
measured.  With  no  shunt,  the  meter  of  course 
indicates  the  current  as  shown  by  its  scale. 
Another  consideration  in  choosing  the  shunt, 
besides  its  resistance,  is  its  physical  size.  The 
shunt  must  be  of  large  enough  carrying  capacity 
that  it  does  not  get  hot  when  passing  its  part  of 
the  current.  If  it  should  get  hot,  its  resistance 
would  change  and  destroy  the  accuracy  of  the 
readings. 

To  use  the  milliammeter  as  a  voltmeter  re- 
quires a  multiplier.  The  latter  is  simply  a  re- 
sistance that  is  connected  in  series  with  the 

80 


meter.  Suppose  the  milliammeter,  with  a  current 
scale  of  o-i  milliamperes,  has  a  resistance  of  3 
ohms.  With  full-scale  deflection,  the  voltage  drop 
across  the  meter  is  o.ooi  amperes  times  3  ohms, 
or  0.003  volts.  Another  way  of  stating  the  re- 
quirement for  full-scale  deflection  of  this  meter 
is,  therefore,  to  say  that  0.003  volts  must  be  im- 
pressed across  it.  When  the  multiplier  is  placed  in 
series  with  the  meter,  its  resistance  causes  a 
voltage  drop,  and  leaves  remaining  a  small  value 
of  voltage  to  operate  the  meter.  By  choosing  the 
right  values  of  series  resistances,  the  meter  can 
be  used  to  measure  a  wide  range  of  total  voltages. 
For  a  meter  resistance  of  RI  ohms  and  a  multi- 
plier resistance  of  R2  ohms,  the  voltage  on  the 
milliammeter  will  be: 


R, 


Ri  +  R: 


x  TOTAL  VOLTAGE. 


The  economy  resulting  from  the  use  of  shunts 
and  multipliers  is  obvious.  A  o-i  Jewell  d.c.  mil- 
liammeter can  be  had  for  $7.50  list.  With  this  one 
meter  as  an  indicator,  as  many  shunts  and  mul- 
tipliers as  desired  can  be  made,  at  a  fraction  of 
the  meter  cost,  and  each  shunt,  or  multiplier,  will 
extend  the  use  of  the  meter. 

The  meter  shown  in  the  photographs  is  de- 
signed to  cover  pretty  well  the  field  of  d.c.  meas- 
urements in  radio.  In  addition,  it  utilizes  a  fixed 
crystal  detector  to  yield  an  instrument  some- 
what similar  to  a  thermo-galvanometer.  While 
it  cannot,  in  the  latter  role,  be  calibrated  to  read 
actual  current  values,  still  it  is  extremely  useful 
in  radio-  and  audio-frequency  measurements, 
for  showing  relative  values,  or  for  indicating  re- 


JUNE,  1928 


FROM  MILLIAMMETER  TO  MULTIMETER 


81 


sonance  or  null  settings.  The  plug-in  system 
which  is  used  makes  it  a  matter  of  seconds  to 
change  from  one  range  to  another,  or  from  volt- 
meter to  ammeter,  or  a.c.  indicator.  In  the  par- 
ticular instrument  shown,  the  layout  provides 
for  five  current  ranges:  o-i  mA.,  o-io  mA.,  o-ioo 
mA.,  o-i  Amp.,  and  0-5  Amps.  The  voltage 
ranges  are  o-io,  o-ioo,  and  o-iooo  volts.  The  a.c. 
indicator  requires  approximately  5  mA.  a.c.  for 
full-scale  reading.  Fig.  i  gives  the  panel  and 
cabinet  layouts. 

In  Fig.  2  is  given  the  diagram  of  connections. 
The  double  plug  is  simple  to  construct.  The 
material  for  it  is  cut  to  shape  as  shown  in  Fig.  i . 
and  then  two  General  Radio  type  274?  contact 
plugs  are  screwed  into  the  two  threaded  3%  slots. 
The  receptacles  for  the  double  plug  consist  of 
General  Radio  type  274]  jacks. 

Only  one  connection  to  the  double  plug  is 
needed  when  the  instrument  is  used  as  a  volt- 
meter or  a.c.  indicator,  so  the  rear  sockets  for 
these  connections  are  left  blank  on  the  panel  top. 
Thus  a  total  of  fourteen  274]  jacks  will  be  neces- 
sary. For  appearance's  sake,  however,  the  blank 
holes  might  be  hidden  by  using  four  more  jacks, 
to  which  no  connections  are  made.  The  negative 
binding  post  is  made  common  for  all  the  functions 
of  the  meter.  It  is  brought  out  at  both  sides  of  the 
panel  to  facilitate  connections.  The  milliammeter 
is  placed  in  the  negative  side  of  the  circuit  so 
that  it  will  be  at  ground  potential  when  the  de- 
vice is  used  as  a  voltmeter.  The  positive  binding 
posts  are  separated  for  the  three  functions  of  the 
meter.  This  makes  for  safety  in  that  it  lessens  the 
chance  of  using  the  ammeter  connection  when 
trying  to  measure  a  voltage.  It  also  allows  con- 
necting the  device  in  the  circuit  to  measure  both 
voltage  and  current,  and  doing  one  or  the  other 
by  changing  only  the  plug.  The  end  of  the  car- 
borundum detector  marked  "A"  by  the  manu- 
facturer goes  to  the  positive  binding  post.  The 
o.ooo5-mfd.  condenser  is  shunted  across  the 
meter  to  protect  it  from  radio-frequency  currents; 
its  use  is  not  an  absolute  necessity,  however. 
The  supports  for  the  shunts,  multipliers,  and 
detector  are  made  of  bus  wire.  The  com- 
mon rear  support  for  the  three  multi- 
pliers is  made  of  sheet  copper  or  tin. 
The  multipliers  used  are  Tobe  Veritas 
5-watt  resistors.  The  power  expended 
in  the  resistor  for  the  higest  range  is 
looo  volts  times  o.ooi  amperes,  or  only 
i  watt,  which  is  sufficiently  low  to 
avoid  heating  the  multiplier. 

The  table  of  Fig.  2  shows  the  shunts 
that  are  used  for  the  different  ranges. 
For  the  lower  ranges,  i.e.,  10  and  100 
milliamperes,  No.  32  tinned  hair  wire 
was  obtained  from  the  hardware  store. 
The  lo-milliampere  shunt  is  so  long 
that  it  must  be  wound  on  a  form,  the 
dimensions  of  which  are  given  in  Fig.  i. 
The  other  shunts  are  short  enough  to  be 
suspended  between  their  bus-wire  sup- 
ports. The  smallest  sizes  of  copper  wire 
consistent  with  freedom  from  heating 
effects  are  used  as  shunts  for  the  higher 
ranges.  Smaller  sizes  than  these  should 
not  be  used;  should  larger  sizes  be 
used,  the  lengths  given  in  the  table 
must  be  increased.  The  lengths  speci- 
fied may  be  slightly  on  the  long  side, 
in  which  case  they  should  be  clipped 
when  calibrating.  All  the  connections 
in  the  instrument  should  be  soldered. 

As  shown  in  the  photograph,  the  con- 
nections between  the  top  panel  and  the 
meter  are  flexible;  thus  the  top  panel 
can  be  turned  over  to  an  easily  ac- 
cessible position  when  adjusting  the 
shunts.  It  is  wise  to  mark  the  sockets 


J 


THE    FINISHED    INSTRUMENT — INSIDE 

plainly  with  the  appropriate  data — 100  Volts, 
i  Ampere,  etc. 

CALIBRATION 

THE  calibration  of  the  meter  is  the  most  im- 
portant part  of  the  job.  The  straightforward 
and  accurate  method  is  to  compare  the  meter 
directly  with  standard  instruments.  It  should  be 
possible  for  the  experimenter  to  obtain  the  use  of 
voltmeters  and  ammeters  from  a  friend,  a  radio 
dealer,  radio  laboratory,  educational  laboratory, 
power  company,  or  other  such  source.  But,  failing 
in  these,  it  is  still  possible  to  obtain  reasonably 
accurate  calibrations.  In  any  case,  the  readings 
of  the  meter  should  not  be  relied  upon  for  greater 
accuracy  than  two  or  three  per  cent. 

To  compare  the  voltmeter  ranges  of  the  device 
directly  with  a  standard  voltmeter,  the  two  in- 


struments  should  be  put  in  parallel  and  con 
nected  to  the  voltage  source,  as  in  Fig.  3.  The 
source  may  consist  of  a  storage  battery  or  dry 
cells,  for  the  ten-volt  range,  and  a  bank  of  B  bat- 
teries, or  a  B  device  for  the  higher  ranges.  Both 
meters  should  be  connected  when  the  readings 
are  made,  and  the  latter  should  be  taken  nearly 
simultaneously.  It  is  not  necessary  to  take  more 
than  three  or  four  points  uniformly  spaced  along 
the  scale.  If  only  one  or  two  readings  are  possible, 
these  should  be  made  near  the  top  of  the  scale. 
On  a  piece  of  graph  paper  a  scale  from  o  to  10 
should  be  drawn  on  the  horizontal  axis,  to  corre- 
spond to  the  meter  scale.  A  scale  from  o  to  1000 
is  drawn  vertically  to  correspond  to  the  readings 
of  the  standard  instrument.  When  the  calibration 
points  for  the  lo-volt  range  are  plotted,  the  verti- 
cal scale  is  assumed  to  run  from  o  to  10,  that  is, 
the  decimal  point  is  placed  by  inspection,  and 
the  curve  is  labeled  o-io  volt  range.  The  points 
for  the  loo-  and  looo-volt  ranges  are  treated 
similarly,  so  that  the  entire  voltmeter  calibration 
is  on  one  sheet.  The  calibration  curves  are  really 
straight  lines  running  through  the  zero  point. 
One  accurate  point  is  sufficient  to  determine  the 
line,  but  more  than  one  serves  as  a  check.  If  all 
the  points  do  not  lie  on  the  line,  the  latter  should 
be  made  to  run  an  average  course  through  them. 
The  calibration  curves  for  the  particular  meter 
shown  are  given  in  Fig.  4.  It  must  be  borne  in 
mind  that  these  curves  will  fit  no  other  meter. 

The  drawing  of  the  calibration  curves  is  neces- 
sitated by  theinaccuraciesof  the  resistance  values 
of  the  multipliers.  The  i -megohm  multiplier 
should  have  yielded  a  full-scale  range  of  1000 
volts,  where  in  fact  it  gave  only  a  range  to  702 
volts.  In  other  words,  its  resistance  is  702,000 
ohms,  and  not  1,000,000  ohms.  Incidentally, 
when  using  a  o-i  milliammeter  as  indicator,  the 
number  of  thousands  of  ohms  in  the  multiplier  is 
equal  to  the  full-scale  range  of  the  voltmeter; 
i.e.,  a  looo-ohm  resistor  gives  a  i-volt  range,  a 
io,ooo-ohm  resistor  a  lo-volt  range,  etc.  The  dis- 
advantage of  the  inaccurate  resistor  is  only  that 
the  calibration  is  not  a  multiple  of  10.  Once  the 


S-de.Vstock 
2  Reou.rtd 


CABINET 


FIG.    1 


Layout  for  panel  and  cabinet  of  the  useful  home  tester  described  here.  The  pho- 
tograph above  shows  the  disposition  of  the  shunts,  meter,  and  fixed  detector 


82 


RADIO  BROADCAST 


JUNE,  1928 


A.C. 


. 

mfd. 


--/VV^VWSAAA-<^ 


Volts 


•  'VWWWWVH§>— 

R3 

VWNAA>V\\VU^)- 
R2 

I  .     ••.fVWWWW> — ©)— 

Ri 


6  volts 
-Amps. or  Mils. 


SHUNTS 

R,  10    mA.      7!*  Feet  No.  32  Tinned  Hair  Wire 
R2  100mA.     4  Inches  No.  32      "      "      " 
R  3  1   Amp.      9  Inches  No.  26  Copper  Wire 
R4  5  Amp.      7  Inches  No.  20     "" 


R5  10  Volts 
Re  100  Volts 
R  7  1000  Volts 


MULTIPLIERS 
Tobe  Veritas 


FIG.  2 

Circuit  connections  and  values  of  apparatus 


instrument  has  been  calibrated,  readings  may  be 
taken  as  accurately  as  with  correct-value  re- 
sistors. If  a  standard  voltmeter  cannot  be  ob- 
tained, new  dry  cells  and  B  batteries  may  be 
used  as  voltage  standards.  The  voltage  of  a 
single  dry  cell  should  be  taken  as  1.58  volts,  and 
that  of  a  22  j-  volt  B  block  as  23.7  volts.  Voltages 
of  larger  blocks  should  be  taken  in  proportion — 
47.4  volts  for  a  45-volt  block,  and  so  on.  Some 
half  dozen  calibration  points  should  be  taken, 
and  the  average  curve  drawn.  The  method  will 
allow  results  of  good  accuracy.  Of  ten  blocks 
whose  voltages  were  measured,  the  maximum 
discrepancy  from  the  voltage  value  given  above 
was  only  0.7  of  a  volt.  Taking  the  average  of 
several  calibration  points  will  tend  to  iron  out 
any  discrepancies. 

In  the  case  of  the  shunts,  their  lengths  can  be 
adjusted  to  make  the  scale  come  out  even,  so 
that  no  calibration  curves  are  necessary.  Al- 
though the  milliammeter  scale  reads  from  o,  0.2, 
0.4,  up  to  I  milliampere,  it  must  be  remembered 
that  with  the  shunt,  say  for  100  milliamperes, 
the  scale  is  read  o,  20,  40,  up  to  100  milliamperes. 
It  is  another  case  of  placing  the  decimal  point. 
To  calibrate  the  meter  and  shunts  by  direct 
comparison  the  meter  is  placed  in  series  with  the 
standard  ammeter,  as  in  Fig.  3.  Suggested  current 
sources  and  loads  for  the  current  calibrations  are 
given.  The  load  resistor  is  adjusted  to  give  full- 
scale  reading  on  the  meter.  If  the  reading  on  the 
standard  ammeter  is  lower  than  the  total  current 
should  be,  first  open  the  load  circuit,  then  melt 
the  solder  and  shorten  the  shunt.  Or  if  the  stand- 
ard meter  reads  high,  lengthen  the  shunt. 
Reclose  the  circuit  and  check  again.  A  few  trials 
will  suffice  to  bring  the  reading  to  the  dot.  If 
the  load  circuit  is  not  opened  before  loosening 
the  shunt,  the  total  current  will  pass  through  the 
meter  and  ruin  it.  Each  shunt  must  be  adjusted 
as  above. 
To  calibrate  the  lo-milliampere  shunt  when 


no  standard  meter  is 
available,  place  the 
meter  in  the  circuit, 
plug  in  on  the  i-milli- 
ampere  range,  and  ad- 
just the  current  to  ex- 
actly i  milliampere. 
Then  plug-in  on  the 
lo-milliampere  range;  if 
the  reading  is  high, 
shorten  the  shunt — or 
vice  versa.  Bring  the 
reading  to  exactly  o.  i 
on  the  scale,  correspond- 
ing to  i  milliampere  on 
the  lo-milliampere 
range.  Finally,  re-check 
the  current  on  the  lower 
range.  For  the  100- 
milliampere  range,  'set 
the  filament  voltage  at 
the  socket  terminals  of 
a  199  type  tube  at  3 
volts.  The  previously 
calibrated  lo-volt  volt- 
meter may  be  utilized. 
Then  with  rheostat  set- 
ting unchanged,  remove 
the  voltmeter  and  place 
the  loo-range  milliam- 
meter in  series  with  the 
filament.  Change  the 
shunt  till  the  meter 
reads  60  milliamperes. 
Again  re-check  the  volt- 
age. The  same  procedure 
may  be  followed  in  cali- 
brating the  i-  and  5- 
ampere  scales,  by  using 
larger  tubes.  The  2OI-A  tube  gives  0.25  am- 
peres at  5  volts,  or  the  112  or  171  tubes  0.50 
amperes  at  the  same  filament  voltage.  For  the 
higher  loads,  several  tubes  in  parallel  can  be 
used,  and  the  currents  added  up.  The  accuracy 
of  this  tube-load  method  is  surprisingly  high. 
Of  four  Radiotron  ux-2oi-A  tubes  picked  at 
random,  the  filament  currents  were  0.250,  0.250, 
0.247,  ar|d  0.249  amperes  at  5  volts.  For  a  ux-i  12 


Amps. or  Mils +Q 
J      Plug      9 J 


10,000  Ohm 
100,000  Ohm 
1  Megohm 


GENERAL  RADIO  PLUGS  AND  JACKS  USED 


Multimeter 


Standard 


VOLTMETER 
CALIBRATION 


it  was  0.500  amperes,  and  for  a  ux-i7i  it  was 
0.493  amperes,  at  the  same  voltage. 

The  a.c.  indicator  is  .the  part  of  the  device 
that  needs  no  calibration.  If  it  were  calibrated, 
the  readings  might  be  50  per  cent,  off  the  next 
day.  It  is,  however,  a  most  convenient  attach- 
ment. With  a  loop  of  wire  connected  to  its  ter- 
minals and  coupled  loosely  to  a  radio-frequency 
circuit,  it  will  show  resonance  points  sharply. 
This  function  is  of  course  applicable  to  wave- 


1100 

/ 

'  / 

VOLT 

1ETEF 

CAU 

BRAT 

ONS 

// 

// 

' 

lOVol 

Rang 

"*S 

VVolt 

uj    fiO( 

§ 

g    500 
400 
300 
200 
100 

/5 

S 

S 

// 

/ 

s 

X 

'/ 

•'m 

a  Volt 

tange 

> 

/ 

S 

X 

/ 

x 

y*      y 

yX 

/ 

X 

0                                       456789        II 

SCALE  READING 


FIG.  4 

Calibration  curves  made  by  the  author  for  me- 
ter used  in  the  original  model.  These  calibrations 
are  not  standard,  varying  with  apparatus  used 
by  the  individual  constructor 


meters.  In  tuning  up  a  crystal-controlled  trans- 
mitter the  indicator  can  be  moved  from  circuit 
to  circuit  down  the  line,  as  the  tuning  progresses, 
and  so  may  save  several  dollars  and  watts  loss 
that  would  be  occasioned  by  the  use  of  radio- 
frequency  ammeters  in  these  circuits. 

The  complete  meter  shows  up  particularly  well 
in  the  measurement  of  B  device  voltages.  It  is  a 
high-resistance  voltmeter — 1000  ohms  per  volt. 
The  current  that  it  draws  at  the  most  does  not 
act  to  give  untrue  voltage  readings. 

An  enumeration  of  the  single  quantities  that 
might  be  measured  in  radio  work  with  the  instru- 
ment would  require  considerable  space,  as  would 
also  detailing  the  connected  experimental  data 
that  are  possible  of  determination  by  its  use. 


Multimeter 


Load 


Standard 


Source 


II 


AMMETER 
CALIBRATION 


CURRENT  CALIBRATION    SOURCES  AND  LOADS: 
10   mA.-  DryCell,400-Ohm  Potentiometer 
100  mA.-  4.5-Volt  Battery,  199-Tube  Filament 
1  Amp.-  6  -  Volt  Battery,  201- A,  171  Tube 
5  Amp.-  6-  Vclt  Battery,  4-Ohm  Rheostat 


FIG.  3 

How  to  calibrate  the 
home-made  meter 
set  with  a  standard 


Output 

Transformer 

Characteristics 


AN  OUTPUT  trans- 
former connecting  a 
loud  speaker  to  a 
power  tube  serves  two 
purposes:  (a.),  to  keep  the  direct  current 
flowing  in  the  plate  circuit  of  that  tube 
from  circulating  through  the  windings 
of  the  loud  speaker;  (6).  to  correct  any 
large  impedance  differences  which  may 
exist  between  the  speaker  and  the  tube. 
The  user  has  a  right  to  expect  that  the 
use  of  the  transformer  will  not  perform 
the  tasks  mentioned  above  at  a  loss  in 
either  power  or  fidelity. 

The  curve  shown  in  Fig.  i  shows  the 
frequency  characteristic  of  the  Pacent 
1:1  output  transformer.  The  upper  curve 
represents  the  voltage  across  5000  ohms 
when  15  volts  were  applied  to  the  grid 
circuit  of  a  210  tube  which  was  properly 
biased  and  taking  about  20  miiliamperes 
of  plate  current.  The  lower  curve  shows 
the  same  characteristic  translated  in 
TU.  Anyone  desiring  to  know  the  power 
delivered  to  the  output  load  resistance 
may  calculate  it  by  dividing  the  voltage 
squared  by  the  resistance.  The  extreme 
variation  obtained  in  this  manner  is  from 
395  milliwatts  at  60  cycles  to  610  milli- 
watts at  2000  cycles,  or  less  than  2  TU, 
which  is  quite  good. 

The  loss  in  power  occasioned  by  the 
use  of  a  transformer  instead  of  placing 
the   loud   speaker  directly   in   the   plate 
circuit  of  the  tube  may  be  calculated  by 
dividing  what  one  actually  gets  into  the 
5000  ohms  by  what  would  be  obtained 
without  the  transformer.  The  power  output  of  a 
tube  working  into  its  own  impedance  (in  this 
case  the  5000  ohms  is  sufficiently  near  that  of  the 
tube)  is  equal  to 


Strays' 


rom 


Wo 


(V-  eg)' 


where 


(i  is  the  amplification  factor  of  the  tube 
eg  is  the  input  volts  r.m.s. 
Rp  is  the  tube  impedance 


Using  this  formula,  the  power  into  5000  ohms 
with  1 5  volts  r.m.s.  on  the  grid  of  the  tube  should 
be  720  milliwatts.  Actually  we  get  only  395  at 
60  cycles  and  610  at  2000  cycles.  These  are  losses 
due  the  transformer  of  only  2.6  and  0.7  TU  re- 
spectively. 

LISTEN  TO  this  from  the 
High  Powered  Radio  World's  Fair:  "'The 

Frets  Releases  last  frontier  of  radio  re- 

sistance will  bow  before  this 
final  stroke  of  air-mastery,  the  automatic  broad- 
cast receiver,'  said  Rear  Admiral  Bradley  Allen 
Fiske,  leading  inventor  of  the  United  States 
Navy  for  the  past  fifty  years,  as  he  declared 
himself  as  being  much  interested  in  the  automa- 
tic broadcast  receiver  which  was  disclosed  to  the 
press  during  the  past  week  by  Harry  N.  Marvin, 
millionaire  inventor  of  Rye,  New  York." 

We  hope  Admiral  Fiske  didn't  say  any  such 
thing  because  the  inventor  of  the  torpedo  plane 
and  the  naval  telescope  sight  which,  again  quot- 
ing from  the  release,  "has  been  adopted  by  all 
the  navies  of  the  world  and  its  use  has  been  the 
main  cause  of  the  improvement  in  accuracy  of 
modern  naval  gunnery,"  should  know  that 
automatic  tuning  has  been  in  use  many  years  in 
the  navy,  commercial,  and  amateur  stations. 

It  is  a  simple  matter  to  change  the  frequency 
to  which  a  station,  or  a  receiver,  is  tuned  by 
pressing  a  button.  How  does  the  Admiral,  or  his 
press  agent,  think  the  frequency  of  wcc,  that 
high-pressure  coastal  station  of  the  Radiomarine 


Corporation  at  Chatham  Massachusetts  is 
changed?  The  operator  is  some  miles  away,  and 
while  there  is  an  attendant  at  the  transmitter, 
does  he  listen  for  a  call  on  the  'phone,  "  Say  bud- 
dy, how's  for  tuning-up  wcc  to  2000  meters?" 
We  have  been  at  Marion,  Massachusetts,  where 
the  transmitter  is  and  have  seen  the  thing  in 
operation.  There  is  a  click  of  a  relay  and  the 
signals  go  out  on  2100  meters,  another  click  and 
the  wavelength  has  been  changed  to  2000  meters, 
another  click  and  the  transmitter  is  turned  off. 
No  one  has  been  near  it  for  an  hour  or  so. 

No,  the  problem  of  turning  on  and  off  your 
receiver,  or  of  changing  its  frequency  setting,  or 
regulating  the  volume  control,  all  from  a  distance 
is  not  new.  Neither  is  the  idea  that  in  the  navy 
in  time  of  war  the  frequency  of  a  transmitter 
could  be  changed  rapidly  and  at  the  will  of  the 
operator.  Such  schemes  are  as  old  as  the  appara- 
tus itself  and  the  business  was  reduced  to  prac- 
tice many  years  ago. 

If  anyone  wants  to  know  how  to  tune  his 
radio  by  pushing  a  button  instead  of  whirling  a 


knob,  we'll  tell  him,  and  at  the  same  time 
give  him  data  on  how  to  turn  the  thing  off 
— in  case  of  sopranos  singing,  for  instance 
— or  to  change  the  volume.  As  a  matter  of 
fact,  the  interested  reader  may  find  an 
article  on  such  matters  in  this  issue.  This 
scheme  is  at  least  old  enough  to  have  gone 
through  the  patent  office,  and  in  these 
days  of  radio  inventions,  this  means  some- 
thing! Incidentally,  Commander  E.  F. 
McDonald  of  the  Zenith  Radio  Corpora- 
tion states  that  his  company  has  acquired 
Mr.  Marvin's  invention  and  that  he,  too, 
believes  the  last  frontier  of  radio  will  bow 
etc.,  etc. 


THE   A.  c.  receiver 

aA.  C-  seems   to    be  causing 

Troubles  dealers  and   service 

men  no  end  of  worry. 
A  dealer  in  New  Hampshire  writes  us 
typical  complaint:  "I.  wish  to  state  that 
the  a.c.  tube  sets  around  this  section  are 
a  decided  failure.  Fluctuating  line  volt- 
ages ruin  tubes  in  a  few  weeks.  I  know 
of  one  individual  that  has  had  four  sets 
of  tubes  this  winter.  I  spent  an  hour  ex- 
plaining why  a.c.  tubes  were  no  good  to 
one  prospective  customer  after  which  he 
agreed  with  me  and  thanked  me.  How- 
ever, the  next  day  he  promptly  went 
to  my  competitor  and  purchased  an 
a.  c.  set." — 

We  should  like  to  point  out  that  the 
trouble  is  by  no  means  altogether  with 
the  a.c.  tube.  For  example,  we  know  an 
editor  of  a  nationally  known  magazine 
who  owns  a  Radiola  17  receiver.  He  lives 
in  a  section  of  New  York  where  line  fluctua- 
tions are  very  severe,  so  severe  in  fact  that 
he  purchases  a  new  171  power  tube  and  a.c. 
tubes,  too,  about  every  two  months.  The  trouble 
here  is  patently  not  with  the  tubes,  but  with 
the  bad  voltage  regulation. 

Any  tube  operated  at  a  temperature  above 
normal  will  not  last  long.  This  means  that  a 
tube  whose  manufacturer  states  should  be  oper- 
ated at  2.5  volts  cannot  be  expected  to  lead  a 
long  or  useful  life  if  the  voltage  about  half  the 
time  is  3.0  volts.  Tubes  operated  from  a.c.  will 
last  a  long  time  if  the  voltage  is  normal  or  slightly 
below. 

From  time  to  time  we  hear  rumors  of  voltage 
adjusting  gadgets  which  are  in  process  of 
development;  units  that  plug  between  the  house 
lighting  socket  and  the  receiver.  Their  duty  is 
to  keep  the  voltage  down  to  some  fixed  figure. 
We  predict  a  million  dollar  business  for  the  first 
reasonably  priced  and  successful  equipment  of 
this  type. 


60 


100 


200 


500     1000 
FREQUENCY 

FIG.    I 


2000 


5000       WPOO 


84 


RADIO  BROADCAST 


May  Standard 

Frequency 

Signals 


STANDARD  FREQUENCY  sig- 
nals from  the  Bureau  of 
Standards  have  been  used  by 
amateurs,  laboratories  and 
experimenters  for  several  years.  These  signals 
are  sent  out  about  the  2oth  of  each  month  and 
begin  at  10:00  p.  M.  E.  S.  T.  On  May  21,  signals 
will  be  sent  on  frequencies  of  650  to  1 500  kc.  and 
should  serve  as  calibrating  signals  for  wavemeters 
and  oscillators  working  in  the  broadcast  range  of 
frequencies.  The  signals  begin  at  10:00  and  con- 
tinue until  1 1 :32  p.  M.  They  consist  of  slightly 
modulated  c.w.  telegraph  and  take  place  as 
follows:  at  10:00  a  general  call  will  be  sent  con- 
sisting of  the  statement  of  the  frequency,  the  call 
letters  of  the  Bureau  station,  wwv,  then  a  series 
of  very  long  dashes  and  call  signals  on  the  stated 
frequency,  then  the  statement  of  the  frequency 
transmitted  and  the  next  frequency.  These 
signals  require  about  8  minutes,  and  are  repeated 
on  the  next  frequency  after  a  lapse  of  four  min- 
utes during  which  the  transmitter  is  adjusted. 

Anyone  within  500  to  1000  miles  of  Washing- 
ton, D.  C.  should  be  able  to  use  the  signals  pro- 
vided he  has  a  receiver  in  which  the  detector  can 
be  made  to  oscillate,  a  Roberts  or  Lab.  Circuit, 
for  example.  The  receiver  should  be  adjusted  to 
the  approximate  frequency,  the  detector  oscillat- 
ing, with  a  pair  of  receivers  in  the  output  of  the 
amplifier  which  may  be  one  or  two  stages.  At 
the  proper  time,  indicated  below,  the  receiver 
should  be  adjusted  until  wwv's  signals  are  heard 
beating  with  the  oscillations  of  the  local  detector 
circuit.  This  circuit  should  then  be  adjusted  to 
zero  beat  with  wwv,  and  a  wavemeter,  preferably 
an  oscillating  tube  attached  to  a  coil  and  con- 
denser, is  tuned  also  to  zero  beat.  The  wave- 
meter  and  the  receiver  and  wwv  are  then  all 
on  the  same  frequency.  A  record  should  be  kept 
of  the  frequency  and  the  setting  of  the  wave- 
meter  condenser  as  well  as  that  of  the  receiver 
in  case  it  is  desired  to  calibrate  the  receiver.  The 
schedule  follows: 


KILOCYCLES 

64,000  to  56,000 

3, 5  50  to    3,500 

2,000  to    1,715 


METERS 
4.69  to      5.35 
84.5    to    85.7 
i  50.0    to  175.0 


E.  S.  T.      MAY  21 
10:00—10:08  P.  M. 
10:12—10:20 
10:24—10:32 
10:36—10:44 
10:48—10:56 
11:00—11:08 
11:12—11:20 
11:24—11:32 

FREQU 
650  ki 
750 
850 
950 
1060 
1200 
1350 
1500 

ENCY       WAVELENGTH 
462  metiers 
400 
353 
316 
283 
250 
222 
200 

GENERAL  ORDER  NO.  24  of 
Short-Ware  the  Federal  Radio  Commis- 

"Nfitt  sion  opens  up  a  new  telegraph 

band  for  amateurs  between 
28,000  and  30,000  kilocycles,  or  9.99  to  10.71 
meters.  It  also  defines  an  amateur  station  as  one 
"operated  by  a  person  interested  in  radio  tech- 
nique solely  with  a  personal  aim  and  without 
pecuniary  interest."  It  also  makes  slight  revisions 
in  the  telephone  bands  open  to  amateur  traffic. 
Radio  telephones  are  now  permitted  to  operate 
in  these  bands: 


NEW    RCA    AIRPLANE    SET 


On  March  173  six-passenger  Stinson-Detroiter 
monoplane  left  Curtiss  Field  on  a  coast-to-coast 
flight  bearing  five  passengers  and  considerable 
radio  equipment.  A  photograph  of  some  of  this 
apparatus,  built  by  the  R.C.A.  is  shown  here.  By 
the  time  this  appears,  many  amateurs  will  have 
worked  the  plane  whose  radio  gear  was  under  the 
key  of  H.  C.  Leuteritz,  and  which  was  licensed  to 
transmit  on  120  meters  using  the  call  letters2XBK. 

Attempts  were  made  to  get  into  contact  with 
the  plane  from  the  RADIO  BROADCAST  magazine 
station,  2  GY,  but  by  the  time  we  got  the  receiver 
wound  up  to  operate  on  the  rather  unusual  wave- 
length of  120  meters,  the  plane  was  apparently 
too  far  away.  We  heard  several  commercial  sta- 
tions calling  her,  and  found  a  lot  of  interesting 
things  going  on  between  100  and  200  meters. 
For  example  the  coast  guard  boats  using  Western 
Electric  radio  equipment  could  be  heard  all  up 
and  down  the  coast  hammering  out  information 
about  the  rum  fleet — probably.  The  stuff  was  in 
code. 

Not  long  ago  we  got  up  at  5  A.  M.  E.  S.  T.  and 
hammered  out  a  CQ  on  our  4O-meter  station, 
2  EJ  (See  our  April,  1927,  issue).  Two  stations 
came  back  at  once,  and  on  about  the  same  fre- 
quency, one  fairly  loud  and  the  other  quite  weak. 
We  clicked  with  the  louder  of  the  two  asking  the 
weaker  to  QRX  for  a  few  minutes.  The  louder  sta- 
tion turned  out  to  be  in  Colorado  and  very  glad 
to  be  QSO  the  east  coast  because  he  was  using 
low  power.  After  some  conversation  we  signed 
off  and  gave  the  weaker  station  a  call,  not  know- 
ing, of  course,  whether  he  was  still  standing-by 
or  not.  Sure  enough  he  came  back,  and  he  too 
was  most  anxious  to  chat.  He  was  using  180  volts 
on  a  1 12  type  tube  and  had  a  call  which  indicated 
he  was  in  Oklahoma.  A  few  days  ago  we  received 
a  card  from  this  operator  stating  that  he  was  on 
a  boat  in  San  Francisco  harbor  on  the  night  in 
question  using  about  i  watt  input  to  his  1 12,  and 
not  having  a  better  one  used  his  Oklahoma  call. 
The  distance  from  San  Francisco  to  Garden  City 
is  something  over  3000  miles  which  is  not  bad 
for  an  input  of  i  watt. 

The  following  letter  from  M.  W.  Pilpel, 
London,  England,  relates  the  success  he  has  had 
with  a  transmitter  described  in  RADIO  BROAD- 
CAST. Mr.  Pilpel's  call  letters  are  6  PP  and  his 
wavelength  is  about  45  meters.  He  states  that 
he  is  on  the  air  every  evening  up  to  about  7  p.  m 
E.  S.  T.  In  this  letter  "NC"  refers  to  a  station 
in  Canada,  "AQ"  to  Iraq,  "AS"  to  Siberia  and 
"FM"  to  Morocco. 

"I  feel  that  I  must  write  and  tell  about 
the  splendid  results  1  have  obtained  with  a 
set  described  in  your  paper. 

The  set  concerned  is  the  "  B  Battery  Trans- 
mitter" described  in  your  November,  1926, 
issue.  I  built  this  set  almost  exactly  as  your 
diagram,  but  used  o.ooo3-mfd.  condensers  in- 
stead of  o.ooo25-mfd.,  and  a  grid  leak  var- 
iable from  1500  to  100,000  ohms  instead 
of  a  fixed  lo.ooo-ohm  one. 

The  plate  supply  is 
from  accumulators, 
180  volts,  and  the  tube 
used  is  a  Marconi  DE5, 
more  or  less  the  Eng- 
lish equivalent  to  your 
ZOI-A.  The  antenna  is 
a  small  cage  with  four 
wires  and  is  only  1 5 
feet  long  and  20  feet 
high.  The  direct 
ground  is  used. 

Now  for  the  results, 
with  an  input  of  27 
m/a  (4.8  watts)  or  less 
I  have  succeeded  in 


JUNE,  1928 

working  four  continents.  Actually  the  best 
distance  worked  is  Manoa,  Pennsylvania 
where  my  friend  NU-3PF  gave  me  R2-3  during 
a  QSO  lasting  nearly  ij  hours.  Two  first  dis- 
trict NUs  have  also  been  worked.  Then,  NC 
(R2-3),  AQ  (Ri!!)  AS  (R3),  and  FM  (R6) 
outside  Europe.  Only  three  European  coun- 
tries possessing  hams  have  not  been  worked 
yet,  Rumania,  Switzerland  and  Lithuania, 
all  others  have  been  worked  on  more  than 
one  occasion.  LPJ  at  Spitzbergen  gave  me  R3 
in  daylight,  and  OIK,  when  400  miles  south  of 
Greenland,  R;.  The  best  miles-per-watt  is 
over  900,  ED  7HJ  of  Bornholm,  Denmark,  750 
miles  away  giving  me  R4  when  using  0.8  watts. 
I  attribute  these  results  chiefly  to  the 
steadiness  of  the  note  emitted  by  the  set  and 
must  congratulate  you  on  bringing  this  excel- 
lent little  "perker"  to  general  notice  and 
describing  it  so  well." 


Recent  Interesting 

Contemporary 

Articles 


EACH  MONTH  we  look 
through  the  welter  of  radio 
magazines  and  papers  that 
come  into  the  office.  Occasion- 
ally, we  read  some  of  them.  QST,  for  example, 
disappears  from  the  office  the  moment  it  comes 
from  the  mail  room  and  does  not  come  back 
until  whoever  took  it  has  perused  every  word. 
Then  someone  else  grabs  it.  Experimental  Wire- 
less and  Wireless  Engineer  (England)  suffers  the 
same  experience.  The  rest  of  them  from  a  tech- 
nician's standpoint,  seem  mediocre,  a  sad  fact 
true  even  of  the  Proceedings  of  the  I.  R.  E.  at 
times.  The  following  recent  articles  are  worth 
reading. 


TITLE  MAGAZINE  DATE 

Double   Detection    Detectors 

and  Screen-Grid  Amplifiers     QST  March 

Directional  Properties  of  An- 
tennas QST  March 
The  Photoelectric  Cell                 Radio                      February 
Frequency    Stabilization    on 

Short    Waves    by    Quartz 

Crystals  L'Onde  Electrique  January 

Theory  of  the  Antenna  Wireless  Exper- 

imenter March 

A  Radio-Frequency  Oscillator    /.  R.  E.  February 

Theory  of  Power  Amplification  I.  R.  E.  February 

Ideals  of  the  Engineer 

by  John  J.  Carty  Journal, 

A.  1.  E.  E.  March 

Use  of  Very  High  Voltage  in 

Vacuum  Tubes  by  W.  D. 

Coolidge  journal, 

A.  1.  E.  E.  March 


IN  SPITE  of  the  fact  that 
Another  Useful  OUT  friend  C.  T.  Burke  of  the 
Publication  General  Radio  Experimenter 

catches  us  up,  publicly, 
whenever  we  make  a  mistake,  we  still  believe 
that  every  serious  radio  thinker  should  be  on  the 
list  of  those  getting  this  excellent  trade  publica- 
tion. 

A  similar  sheet  has  arrived  in  the  Laboratory. 
It  is  called  the  Aerovox  Research  Worker  and  is 
published  by  the  Aerovox  Wireless  Corporation, 
70  Washington  Street,  Brooklyn,  New  York. 
It,  too,  is  worth  having  regularly.  In  our  list  of 
"Manufacturers'  Booklets  Available,"  regularly 
listed  in  the  back  advertising  pages  of  this 
magazine  this  publication  is  listed  as  No.  120. 

ANYONE  WANTING  a  free 
Radio  School  ticket  to  the  Radio  Institute 

Scholarships  of    America    should    get    in 

touch  with  J.  V.  Maresca, 
Room  1889,  Hotel  Roosevelt,  New  York.  He 
has  charge  of  applications  for  two  scholarships 
offered  by  the  Veteran  Wireless  Operators' 
Association  and  the  two  offered  by  A.  H.  Grebe. 
Awards  will  be  made  to  those  American  born 
youths  over  eighteen  years  of  age  who  write  the 
best  letters  of  essays  on  "Why  the  American 
Merchant  Marine  Needs  Perfect  Wireless  Com- 
munication." 

— KEITH  HENNEY. 


New    Apparatus 


An  Inside  Antenna 


Device:  INDOOR  AERIAL.  Consists  of  a  seventy- 
foot  spool  of  indoor  aerial  wire,  a  twenty-five  foot 
length  of  rubber-covered  ground  wire,  and  a 
ground  clamp.  The  aerial  wire  is  made  of 
stranded  copper  covered  with  a  brown  braid. 
Manufactured  by  the  BELDEN  MANUFACTURING 
COMPANY.  Price:  $1.55. 

Application:  Designed  especially  for  indoor 
antennas,  the  wire  is  flexible  and  can  be  easily 
wired  around  a  room,  over  window  frames,  and 
because  of  the  neutral  brown  color  of  the  braid, 
the  wire  is  practically  invisible. 

Fine  New  Drum  Dial 

Xji 

Device:  NATIONAL  TYPE  F  VELVET  VERNIER 
DRUM  DIAL.  Dial  light  is  readily  removable, 
and  has  both  terminals  insulated  from  the  dial. 
Dial  numbers  are  engraved  on  strip.  Drum  is 
made  of  brass,  with  nickel  plating  and  the  dial 
front  is  silver  plated.  The  movement  has 


NATIONAL    DRUM    DIAL 

absolutely  no  back-lash.  Manufactured  by  THE 
NATIONAL  COMPANY.  Price:  $4.50. 
Application:  May  be  used  in  constructing  any 
receiver.  One  of  the  best  drum  dials  that  have 
been  received  in  the  laboratory. 

A  Good  Phonograph  Pick-U-p 

X32 

Device:  Amplion  Phonograph  Pick-Up  Unit. 
Device  is  complete  with  tone  arm  and  volume 
control.  Manufactured  by  the  AMPLION  COM- 
PANY. Price:  $15.00. 

Application:  To  be  used  in  conjunction  with  a 
phonograph  turn-table  and  an  audio  amplifier 
to  make  possible  the  electrical  reproduction  of 
phonograph  records.  The  tone  arm  is  screwed 
down  on  the  turn-table  bed  of  the  phonograph  in 
such  a  position  that  the  unit  on  the  end  of  the 
tone  arm  can  be  correctly  placed  on  a  record. 
The  Laboratory's  sample  of  this  pick-up  has 
given  very  satisfactory  reproduction  of  records 
and  it  has  the  advantage  over  some  other  pick- 
ups that  it  exerts  but  slight  pressure  on  the  rec- 
ord resulting  in  less  record  wear. 

Resistor  for  the  Screen-Grid  Tube 

*33 

Device:  AMPERITE  No.  622.  Filament-control 
resistance  for  screen-grid  tubes.  When  placed  in 
series  with  the  tube  filament  and  a  six-volt 
battery,  this  resistance  will  reduce  the  voltage  to 
3.3  volts,  the  correct  voltage  for  a  screen-grid 
tube.  Manufactured  by  the  RADIALL  Co.  Price: 
$1.10. 

Application:  May  be  used  for  filament  control 
of  the  screen-grid  type  tubes  in  a  receiver. 


Amperites  for  each  type  of  tube  are  made. 
Complete  data  on  the  different  styles  available 
may  be  obtained  by  writing  the  manufacturer 
through  RADIO  BROADCAST. 

Set  Tester  of  Wide  Use 

X34 

Dei-ice:  RADIO  SET  TESTER,  A.  C  AND  D.  C. 
MODEL  537.  This  set  tester  is  designed  for  the 
testing  of  all  kinds  of  radio  receivers  operated 
from  either  alternating  or  direct  current  light 
socket  power  or  from  batteries.  It  will  measure 
the  various  voltages  used  in  the  radio  set  both 
at  the  tube  sockets  or  at  any  part  of  the  set;  it 
will  test  continuity  of  circuits,  and  test  the  tubes 
under  the  same  conditions  as  exists  when  in  their 
sockets.  All  tests  can  be  made  by  using  the  volt- 
ages normally  supplied  to  the  set  by  its  batteries 
or  socket  power  with  no  change  in  connections, 
so  that  no  auxiliary  power  supply  is  required. 
Socket  adapters  are  supplied  so  that  uv,  ux 
and  UY  type  tubes  may  be  tested. 

All  of  these  tests  are  possible  using  the  two 
meters  contained  in  the  instrument,  which  are  an 
a.  c.  voltmeter  having  three  ranges  150,  8,  and  4 
volts,  and  a  d.  c.  volt-milliammeter  which  has 
four  voltage  ranges,  (600,  300,  60,  and  8  volts) 
and  two  current  ranges,  (150  and  30  milliam- 
peres).  The  voltmeter  has  a  resistance  of  1000 


AMPLION    PHONOGRAPH    PICK-UP 

ohms  per  volt  and  can  therefore  be  used  satis- 
factorily to  measure  the  output  voltages  of  B 
power  units.  Tests  on  tubes  can  also  be  made 
independent  of  any  radio  receiver  by  connect- 
ing a  plug  supplied  with  the  instrument  into  a 
light  socket. 


r)  ROpUCTS  of  radio  manufacturers  whether 
1  new  or  old  are  always  interesting  to  our 
readers.  These  pages, a  feature  of  RADIO  BROADCAST 
explain  and  illustrate  products  which  have  been 
selected  for  publication  because  of  their  special 
interest  to  our  readers.  This  information  is  pre- 
pared by  the  Technical  Staff  and  is  in  a  form  which 
we  believe  will  be  most  useful.  We  have,  wherever 
possible,  suggested  special  uses  for  the  device  men- 
tioned. It  is  of  course  not  possible  to  include  all 
the  information  about  each  device  which  is  avail- 
able. Each  description  bears  a  serial  number 
and  if  you  desire  additional  information  direct 
from  the  manufacturer  concerned,  please  address  a 
letter  to  the  Service  Department,  RADIO  BROAD- 
CAST, Garden  City,  New  York,  referring  to  the 
serial  numbers  of  the  devices  which  interest  you 
and  we  shall  see  that  your  request  is  promptly 
handled. — THE  EDITOR. 


Manufactured  by  the  WESTON  ELECTRICAL 
INSTRUMENT  CORP.  Price:  Sioo. 
Application:  An  essential  instrument  for  the 
radio  dealer  and  the  professional  radio  service 
man,  for  it  makes  possible  the  thorough,  accurate 
and  rapid  testing  of  a  receiver. 

For  the  250  Type  Tube 


. 

Device:  Power  Equipment  for  the  250  type  tube. 
The  apparatus  listed  below  has  been  designed 
for  the  250  type  tube.  This  tube  requires  much 
more  plate  current  than  other  types  of  power 
amplifier  tubes  and  therefore  the  apparatus  for 
use  with  it  must  be  constructed  to  prevent 
overheating  and  saturation  effects  at  high 
currents. 

TYPE  565-6  FULL-WAVE  TRANSFORMER. 
Designed  for  full-wave  rectrfication  using  two 
type  281  tubes.  The  plate  voltage  winding  is 
1  200  volts  with  a  center  tap.  There  are  also  two 


WESTON    SET   TESTER 

7-5-volt   secondaries   for   the   filaments  of   the 
rectifier  and  power  amplifier  tubes.  Price :  $20.00. 

TYPE  565-A  HALF-WAVE  TRANSFORMER.  This 
transformer  is  designed  for  half-wave  rectifica- 
tion in  conjunction  with  one  281  type  tube. 
There  are  four  secondaries:  one  of  600  volts  for 
the  plate  voltage;  two  of  7.5  volts  each  for  the 
filaments  of  a  rectifier  and  power  amplifier  tubes; 
and  one  of  2.5  volts  for  the  filaments  of  226  and 
227  type  of  tubes  in  case  this  transformer  is  in- 
corporated in  a  complete  two-  or  three-stage 
amplifier.  Rated  at  200  watts.  Price:  $20.00. 

TYPE  5&7-A  SPEAKER  FILTER.  A  speaker 
filter  that  thoroughly  insulates  the  speaker 
from  the  high  plate  voltage  and  current  of  the 
last-stage  tube.  The  choke  used  is  of  unusually 
heavy  construction  and  has  an  inductance  of 
approximately  15  henries  and  a  continuous  cur- 
rent rating  of  100  milliamperes.  The  direct  cur- 
rent resistance  is  250  ohms.  Two  microfarad 
condensers  are  used  on  each  side  to  completely 
insulate  the  speaker  from  high  voltage.  Connec- 
tions to  the  input  side  are  in  the  form  of  leads 
while  the  speaker  is  connected  to  two  binding 
posts.  Price:  $10.00. 

TYPE  527-A  RECTIFIER  FILTER.  This  unit 
consists  of  a  combination  of  two  heavy-duty 
chokes  with  an  inductance  of  approximately  13 
henries  each  and  a  continuous  current  rating 
of  100  milliamperes  and  a  condenser  assembly 
consisting  of  a  4-2-4~mfd.  combination  rated 
at  1000  volts  d.  c.  The  direct  current  resistance 
of  each  choke  is  175  ohms.  Price:  $25.00. 

All  the  above  apparatus  Manufactured  by  the 
GENERAL  RADIO  COMPANY. 
Application:  This  apparatus   may   be   used   in 


86 


RADIO  BROADCAST 


JUNE,  1928 


constructing  power  amplifiers  using  the  250  type 
tube  especially,  although  the  equipment  is  of 
course  suited  to  the  construction  of  any  power 
unit  from  which  it  is  desired  to  obtain  compara- 
tively large  amounts  of  current,  say  60  milliam- 
peres  or  more. 

Dynamic  Speaker  Models 


Device:  JENSEN  DYNAMIC  SPEAKER:  A  moving- 
coil  type  loud  speaker.  It  may  be  connected 
directly  to  the  output  of  a  receiver  without  any 
need  of  an  output  device,  for  the  transformer 
contained  within  the  loud  speaker  insulates  the 
windings  of  the  moving  coil  from  the  plate  cur- 
rent of  the  power  tube.  The  field  winding  of  the 
speaker  must  be  supplied  with  energy  from  an  A 
battery  (Model  D-44),  or  from  a  go-volt  d.  c. 
source  (Model  0-45)  or  from  the  I  lo-volt  a.  c. 
mains  (Model  0-44.  a.  c.).  Manufactured  by 
the  JENSEN  RADIO  MFG.  Co. 
Price:  Model  0-44,  $65.00;  Model  0-45,  $67.50; 
Model  D-44-AC.  $75.00. 

Application:  A  sample  of  this  loud  speaker  has 
been  in  use  in  the  Laboratory  for  some  time  and 
has  proved  to  be  an  excellent  instrument.  An 
elementary  diagram  of  the  loud  speaker  appears 


Intense  magnetic 


Circular  paper  cone 
specially  treated  '••• 


Field  connections  to 
storage  A  Battery 
D.C.6Volts-0.4Amp. 
or  A  C.6  Volts,  rectified 
and  filtered 


>• 8H  depth  overall 

DIAGRAM   OF   JENSEN    CONE 

herewith.  The  cross-sectioned  part  represents  a 
magnet,  energized  by  the  current  flowing  through 
the  field  winding.  As  a  result  there  is  produced 
across  the  gap  in  the  magnet  an  intense  magnetic 
field.  The  paper  cone  is  arranged  as  indicated, 
projecting  into  the  gap,  and  around  this  portion 
of  the  cone  is  wound  a  small  coil  of  wire.  This 
coil  is  connected  to  the  secondary  of  the  step- 
down  transformer,  the  primary  of  which  con- 
nects to  the  output  of  the  radio  receiver.  The 
signal  currents  flowing  through  the  coil  react 
with  the  magnetic  lines  of  force  flowing  across 
the  gap  and  produce  a  torque  which  makes  the 
coil  move  left  and  right.  The  cone,  attached 
solidly  to  the  moving  coil,  must  also  move  with 
the  coil  and  its  movements  produce  the  sounds. 
This  loud  speaker  gives  best  results  when 
operated  in  conjunction  with  a  large  baffle  but 
will  also  work  very  well  in  the  cabinet  supplied 


(F) 


CIRCUITS    FOR   CENTRALAB    VOLUME    CONTROLS 


by  the  Jensen  Company.  The  cone  unit  can  also 
be  purchased  without  the  cabinet  for  installa- 
tion in  radio  or  phonograph  consoles. 

Resistors  for  A.  C.  Sets 

X37 

Device:  VOLUME  CONTROL  RESISTANCES,  for 
a.  c.  receivers.  The  method  of  volume  control 
commonly  used  in  d.  c.-operated  receivers,  i.  e.,  a 
filament  rheostat  in  the  filament  circuit  of  the 
r.  f.  tubes,  cannot  be  applied  to  a.  c.  circuits 
because  lowering  the  filament  potential  of  226 
type  tubes  will  tend  to  produce  a  hum  in  the 
loud  speaker  and  because  with  227  type  tubes 
the  emission  from  the  heater  will  lag  behind 
changes  in  the  current  through  the  heater  fila- 
ment. It  is  therefore  necessary  to  use  some  other 
type  of  volume  control.  The  devices  listed  below 
will  be  found  very  satisfactory. 

RX-ioo  Radiohm,  a  special  tapered  resistance 
for  use  across  the  secondary  of  one  of  the  r.  f. 
transformers,  preferably  the  detector  stage.  See 
Fig.  I -A.  Price;  $2.00. 

RX-O25  Radiohm,  a  special  tapered  resist- 
ance for  use  as  a  volume  control  across  the 
primary  of  an  r.  f.  transformer  or  across  the 
primary  of  a  tuned  antenna  coil.  See  Fig.  i-B. 
Price:  $2.00. 

P-H2  Potentiometer.  A  6ooo-ohm  potentiom- 
eter with  a  special  tapered  resistance  at  the 
end  to  be  used  in  the  antenna  circuit  or  across 
the  primary  of  a  tuned  r.  f.  stage.  See  Fig.  i-C. 
Price:  $2.00. 

M-5oo  Modulator.  A  potentiometer  with  a 
special  tapered  resistance  for  the  grid  circuit 
of  one  of  the  audio  stages.  Used  principally  as  an 
auxiliary  control  in  a.  c.  circuits.  See  Fig.  i-D. 
Price:  2.00. 

HP-O5O  Heavy  Duty  Potentiometer.  A  wire- 
wound,  non-inductive  potentiometer  used  as  a 
plate  circuit  control.  See  Fig.  i-E.  Pricf:  $2.00. 

PR-O5O  Power  Rheostat.  A  specially  con- 
structed rheostat  to  carry  heavy  currents  and  an 


excellent  control  for  use  in  the  primary  of  a 
power  transformer.  See  Fig.  i-F.  Price:  $1.25. 
All  of  the  above  units  are  manufactured  by  the 
CENTRAL  RADIO  LABORATORIES. 
Application;  The  application  of  these  units  to 
a.  c.  circuits  has  been  covered  in  the  data  given 
above.  A  useful  pamphlet  is  obtainable  from  the 
manufacturers  through  RADIO  BROADCAST  de- 
scribing these  units  in  detail  and  giving  further 
information  regarding  the  circuits  in  which  they 
are  to  be  used. 


TRUVOLT   RESISTORS    AND    BELDEN    ANTENNA    KIT 


JENSEN    DYNAMIC   CONE 

Resistors  for    Power    Supply    Use 

X38 

Device:  TRUVOLT  RESISTORS.  Wire-wound  resis- 
tors, using  Nichrome  wire  wound  on  an  asbestos 
covered  enamel  core.  Available  as  fixed  and 
variable  resistors  as  follows: 

TYPE  T,  variable  resistors,  with  maximum 
resistances  of  200  to  50,000  ohms. 

TYPE  B,  fixed  resistors,  rated  at  25  watts, 
and  available  in  sizes  from  200  to  50,000  ohms. 

TYPE  C,  fixed  resistors,  rated  at  50  watts, 
and  available  in  sizes  from  200  to  100,000  ohms. 

TYPE  D,  fixed  resistors,  rated  at  75  watts, 
and  available  in  sizes  from  200  to  100,000  ohms. 

TYPE  V,  center-tapped  fixed  resistors,  available 
in  sizes  from  10  to  200  ohms,  and  designed  es- 
pecially for  use  as  center-tapped  resistors  across 
the  filaments  of  a.  c.  tubes. 

GRID  RESISTORS,  available  in  sizes  from  10 
to  2000  ohms,  and  designed  especially  for  use  as 
grid  suppressors,  in  radio-frequency  amplifiers. 

SPECIAL  TAPPED  FIXED  RESISTORS,  designed 
for  use  with  the  popular  types  of  power  packs 
such  as  those  made  by  Silver-Marshall,  Amer- 
tran,  Samson,  Thordarson,  etc. 

Manujactured  by  ELECTRAD,  INC.  Prices:  vary 
according  to  the  style  and  rating  of  resistors. 
Application:  The  Truvolt  line  of  resistors  is  very 
complete  and  units  are  available  to  meet  almost 
every  need  in  the  construction  of  radio  receivers 
and  power  packs.  Complete  data  can  be  ob- 
tained from  the  manufacturer  through  RADIO 
BROADCAST. 


LIFE  FOR  A  WEAK  RECEIVER 

The  screen-grid  tube  can  be  added  to  any  receiver,  and — at  the  cost  of  one 
additional  control— will  add  a  respectable  amount  of  sensitivity  and 
some  selectivity.  Directions  are  given  for  using  this  unit  with  any  receiver 

A  Screen-Qrid  Booster  Unit  for  Any  Receiver 


THE  introduction  of  the  screen-grid   tube 
has  opened  a  new  field  in  r.f.  amplification, 
for  not  only  does  this  tube  make  possible 
at  broadcast  frequencies  an  amplification  much 
greater  than  is  possible  with  a  2OI-A  type,  but 
because  of  its  very  small  capacity  between  con- 
trol grid  and  plate,  relative  stability  as  an  r.f. 
amplifier  is  secured. 

As  most  experimenters  know,  the  screen-grid 
tube  has  two  grids,  one  forming  a  nearly  complete 
shield  around  the  plate  and  known  as  the  screen 
grid,  while  the  other  is  practically  the  same  as 
the  grid  in  the  ordinary  tube,  and  is  called  the 
control  grid.  The  screen-grid  has  two  effects;  it 
shields  the  plate  as  its  name  indicates,  and  also 
increases  the  mutual  conductance  in  such  a 
manner  that  the  amplification  of  the  tube  may 
be  at  some  frequencies  as  high  as  100.  The  func- 
tion of  the  control  grid  is,  as  in  the  2OI-A  tube, 
to  regulate  the  flow  of  electrons  between  fila- 
ment and  plate. 

The  construction  of  the  tube  may  be  seen  in 
the  accompanying  photographs.  The  metal  cap 
on  top  of  the  tube  is  the  terminal  for  the  control 
grid  while  the  prong  on  the  socket,  marked 
"grid,"  is  the  terminal  for  the  screen-grid.  These 
connections  should  be  carefully  noted. 


By  Glenn  H.  Browning 

Browning-Drake  Corporation 

To  get  the  utmost  from  the  screen-grid  tube 
involves  careful  shielding  of  the  tube  and  the 
circuit  in  which  it  is  used.  There  are  thousands 
of  sets  which  are  not  now  shielded  nor  could  they 
readily  be  shielded.  This  difficulty,  in  addition 


R.  BROWNING'S  "booster"  provides  at  one 
time  a  means  of  improving  the  TJX  ability 
of  any  receiver  and  its  selectivity.  In  the  Laboratory, 
it  was  possible  to  hear  stations  that  were  not  audible 
without  it.  It  was  also  possible  here  to  listen  to  KDKA 
with  very  little  interference  from  WABC,  only  8 
miles  away,  while  under  usual  conditions  this  is  not 
•possible  at  all.  In  our  estimation,  this  booster  should 
be  a  gold  mine  to  service  men — because  nearly  every 
one  wants  some  little  gadget  like  this  that  will  make 
an  otherwise  almost-dead  receiver  come  to  life. 

We  hope  that  Mr.  Browning  will  design  a  set 
of  plug-in  coils  so  that  this  single  stage  of  r.f. 
amplification  may  be  used  with  short-wave  receivers. 
It  will  then  eliminate  nearly  all  radiation  from 
these  receivers,  as  well  as  improve  signal  strength. 
— THE  EDITOR. 


to  the  fact  that  it  is  very  rare  indeed  that  any 
existing  circuit  can  be  efficiently  and  easily  al- 
tered for  the  successful  use  of  the  screen-grid 
tube  makes  it  wiser  in  most  cases  to  find  ways 
of  utilizing  the  high  gain  to  be  secured  from  the 
screen-grid  tube  elsewhere  than  in  the  receiver 
proper. 

For  the  last  year  there  has  been  an  insistent 
demand  for  another  stage  of  tuned  radio- 
frequency  amplification  to  be  added  to  the 
Browning-Drake  receivers.  The  writer  has 
worked  a  great  deal  on  this  problem  only  to  come 
to  the  conclusion  that  it  was  not  feasible  for  the 
home-builder  because  of  the  high  gain  in  the 
Browning-Drake  transformers  which  entails 
careful  construction,  and  critical  adjustment  of 
the  neutralizing  condensers.  However,  with  the 
availability  of  the  screen-grid  tube,  the  problem 
simplifies  itself  considerably. 

For  some  time  the  writer  has  been  experiment- 
ing with  a  one-stage  r.f.  amplifier  which  could 
be  added  to  the  large  number  of  Browning-Drake 
sets  which  are  in  use.  This  amplifier  employs 
the  screen-grid  tube,  and  not  only  gives  a  tre- 
mendous r.f.  amplification,  but  increases  selec- 
tivity to  a  marked  degree.  It  has  also  been 
found  that  the  one-stage  amplifier  can  be  used 


RADIO  BROADCAST 


JUNE,  1928 


B-M5 


Leave  ground 
connected  to  Receiver 


Ant.  on  Set 
of  Receiver 


O 

B+90 

CIRCUIT   OF   THE    BOOSTER   UNIT 

The  antenna  connection  indicated  will  work  with  all  Browning-Drake  type  receivers  • 

with  others,  it  is  best  to  connect  the  antenna  lead  to  the  set  directly  to  the  stator 

plates  of  the  first  tuning  condenser 


not  only  on  Browning-Drake  sets,  but  on  any 
existing  receiver,  simply  by  making  a  connection 
to  the  stator  plates  of  the  first  tuning  condenser. 
[The  lead  from  the  "booster"  may  be  connected 
to  the  antenna  posts  of  some  receivers,  but  not 
all,  and  it  is  best  to  follow  the  suggestion  here 
which  is  certain  to  work. — EDITOR.]  By  using  this 
one-stage  device,  the  writer  has  received  signals 
that  were  inaudible  before. 

The  assembly  of  the  one  stage  screen-grid 
booster  is  quite  simple.  The  Browning-Drake 
Corporation  furnishes  a  kit  consisting  of  the 
coil,  condenser  and  dial,  together  with  a  set  of 
aluminum  shields,  a  radio-frequency  choke,  a 
four-wire  cable,  lo-ohm  resistances  and  the 
mounting  hardware,  and  all  that  is  necessary  for 
the  constructor  to  purchase  is  a  tube  socket,  and 
the  three  following  condensers;  a  j  mfd.,  a  o.oooi 
mfd.  and  a  0.00025  mfd. 

The  picture  wiring  diagram  and  the  schematic 
wiring  diagram  are  presented  on  this  page.  It 
should  be  noted  that  the  stator  plates  of  the 
tuning  condenser  go  to  the  top  of  the  screen-grid 
tube.  The  two  lo-ohm  resistances,  put  in  as  in- 
dicated, cut  down  the  six  volts  from  the  storage 
battery  to  3.3  volts  which  is  the  correct  voltage 
for  the  screen-grid.  It  is  noted  that  the  one-stage 
booster  is  run  from  a  battery  as  the  writer  does 
not  believe  it  feasible  to  light  the  filament  of  the 
cx-322  from  raw  a.c.  In  using  the  one-stage 
booster  on  any  Browning-Drake  assembly,  all 
that  is  necessary  to  do  is  to  disconnect  the  an- 
tenna from  the  set,  connect  it  to  the  antenna  post 
of  the  booster,  which  is  shown  on  the  left,  and 
to  connect  the  wire  lead,  which  is  on  the  right 
of  the  booster  to  the  antenna  post  on  the 
Browning-Drake  receiver.  The  ground  is  left  in 
its  position  on  the  set  proper.  From  the  wiring 
diagrams,  it  may  be  noted  that  a  filament  switch 
is  inserted  in  the  pIus-A  battery  lead  to  control 
the  filament  of  the  cx-322  tube.  This  makes  the 
separate  amplifier  unit  independent  of  the  re- 
ceiving set  proper  and  permits  it  to  be  used  on 
any  radio  set.  When  using  the  booster  on 
Browning-Drake  receivers,  particular  care  should 
be  taken  that  the  set  is  well  neutralized  before 


adding  the  booster.  Volume  may  be  controlled 
as  before  on  the  receiving  set. 

HOW   TO   CONNECT   THE    BOOSTER 

VA/HEN  using  this  one-stage  booster  with 
*  other  receivers,  the  wire  on  the  right  of 
the  shield  casing,  is  connected  to  the  stator 
plates  on  the  first  tuning  condenser.  The  other 
connections  are  unchanged,  except  that  the 
antenna  lead  is  connected  to  the  proper  post  on 
the  booster.  The  operation  of  the  booster  is  very 
simple  indeed  as  all  that  is  necessary  to  do  is  to 
tune-in  the  receiver  by  means  of  the  regular 
control  and  then  tune  the  booster. 

Tuning  on  the  booster  unit  is  not  extremely 
critical  though  it  increases  the  selectivity  of  the 
set  in  a  marked  degree.  The  antenna  used  on  the 
receiver  when  this  booster  is  employed  should 
be  very  short,  in  fact,  not  more  than  25  to  40 
feet,  and  as  nearly  vertical  as  possible.  The 
vertical  antenna  will  pick  up  relatively  a 
stronger  signal. 

LIST   OF    PARTS 

i  Browning-Drake  Booster  322  Kit  assembly. 
(Includes  shields,  the  coil  and  tuning 
condenser  with  dial,  two  lo-ohm  resist- 
ances, a  four-wire  cable,  shield  wire,  and 
r.f.  choke). 

i     ux  tube  socket. 

I     o.oooi-mfd.  mica  Condenser. 

i     j-mfd.  mica  Condenser. 

i     o.ooo25-mfd.  Condenser. 


00025  mfd 


To  Antenna 
on  Set 


A    PICTURE    DIAGRAM 
How  to  connect  the  various  parts  em- 
ployed and  the  recommended  layout 


.  . 


Our  Readers  Suggest 


9  9 


OUR  Readers  Suggest"  is  a  clearing  house 
for  short  radio  articles.  There  are  many 
interesting  ideas  germane  to  the  science  of  radio 
transmission  and  reception  that  can  be  made  clear 
in  a  concise  exposition,  and  it  is  to  these  abbrevi- 
ated notes  that  this  department  is  dedicated.  While 
many  of  these  contributions  are  from  the  pens  of 
professional  writers  and  engineers,  we  particularly 
solicit  short  manuscripts  from  the  average  reader 
describing  the  various  "kinks,"  radio  short  cuts, 
and  economies  that  he  necessarily  runs  across  from 
time  to  time.  A  glance  over  this  "Our  Readers  Sug- 
gest" will  indicate  the  material  that  is  acceptable. 

Possible  ways  of  improving  commercial  appara- 
tus is  of  interest  to  all  readers,  The  application  of 
the  baffle  board  to  cone  loud  speakers,  is  a  good 
example  of  this  sort  of  article.  Economy  "kinks," 
such  as  the  spark-plug  lightning  arrester,  are  most 
acceptable.  And  the  Editor  will  always  be  glad  to 
receive  material  designed  to  interest  the  experi- 
mental fan. 

Photographs  are  especially  desirable  and  will  be 
paid  for.  Material  accepted  will  be  paid  for  on  pub- 
lication at  our  usual  rates  with  extra  consideration 
for  particularly  meritorious  ideas. 

— THE  EDITOR. 


An  Emergency  Detector  B  Supply 

IT  HAS  been  my  experience  that  the  voltage 
distributing  resistor  system  in  the  average  B- 
power  unit  is  the  weak  point  of  these  devices. 
On  several  occasions  the  resistor  passing  the 
current  to  the  detector  tube  in  my  receiver  has 
gone  bad.  I  found  that  an  emergency  connection 
could  be  effected  in  a  few  seconds,  by  wiring  an 
outside  resistor  from  the  "detector  B"  post  on 
the  set  to  the  "amplifier  B"  post  on  the  unit. 
A  ioo,ooo-ohm  resistor  is  about  the  correct 
value.  The  set  works  quite  as  well  operating  the 
detector  tube  from  the  90  volts  power-unit  tap, 
through  the  external  resistor,  as  it  did  from  the 
original  "detector  B"  supply  post. 

I  rigged  up  the  resistor  mounting,  shown  in 
Fig  I,  to  enable  me  to  try  different  values  of 
resistors.  The  mounting  is  wired,  as  shown,  to 
the  "amplifier  B"  positive  post,  and  the  detector 
lead  is  caught  under  the  Fahnestock  clip. 

PERRY  WHITE.  New  York  City. 


STAFF   COMMENT 

j  N  SOM  E  cases  it  may  be  desirable  to  bypass 
*  this  extra  resistor.  This  can  generally  be  ac- 
complished by  leaving  the  lead  to  the  "detector 
B"  post  on  the  set  (now  wired  to  the  special  re- 
sistor) also  connected  to  the  original  "detector 
B  "  supply  post  on  the  power  unit,  taking  advan- 
tage of  the  bypass  condenser  included  in  that 
circuit.  As  the  faulty  resistor  is  probably  "  open  " 
this  will  have  no  effect  on  the  potential.  If  de- 
sired, the  resistor  may  be  bypassed  by  connecting 
any  convenient  condenser  from  i.o  mfd.  up. 
across  the  resistor.  It  is  also  possible  to  connect 
the  external  resistor  directly  across  the  "am- 
plifier B"  plus  and  the  "detector  B"  plus  posts 
on  the  receiver  itself,  without  going  back  to  the 
power  supply  unit. 
The  clip-wired  Clarostat  and  the  clip-wired 


FIG.    1 

This  simple  arrangement  can  be  used  to  supply 

either  detector  or  intermediate-amplifier  plate 

potential  from  a  high  voltage  tap  in  the  case 

of  resistor  break-down. 


FIG.    2 

The  use  of  clip  connectors  permanently  fastened 

to  flexible   leads   for  condensers   and   resistors 

greatly  facilitates  experimental  and  emergency 

work  for  many  uses  around  the  radio  set 

bypass  condensers  suggested  by  Mr.  Graham, 
elsewhere  in  this  department,  are  particularly 
convenient  in  effecting  temporary  arrangements 
of  this  kind. 

Emergency  and'  Experimental 
Connections 

IN  MY  experimental  work,  as  well  as  in  emer- 
*  gency  set-ups  in  the  perpetual  endeavor  to 
keep  the  family  set  functioning  properly,  I  have 
found  it  very  convenient  to  have  a  complete  set 
of  parts  available  for  immediate  connection  by 
means  of  clips.  The  idea,  illustrated  by  a  few  of 
the  parts  so  arranged,  is  made  clear  in  the  accom- 
panying photograph  (Fig.  2.). 

The  clips  used  are  of  the  small  battery  type, 
obtainable  at  most  electrical  afid  radio  supply 
houses.  Any  type  of  ordinary  hook-up  wire  may 
be  used  for  the  leads — I  used  flexible  Celatsite. 
In  the  cases  of  certain  parts,  such  as  the  con- 
densers which  already  have  long  and  flexible 
leads,  these  may  be  soldered  directly  to  the  clips. 

The  following  parts  which  I  happened  to  have 
on  hand,  were  arranged  with  two-foot  leads  and 
clips: 

I     Volume  control   Clarostat   (variable   re- 
sistor) 

89 


i  Universal   range  Clarostat   (variable  re- 
sistor) 

i  Low  range  Clarostat  (variable  resistor) 

I  Amsco  2ooo-ohm  Duostat 

1  40O-ohm  potentiometer 

2  Fixed  condensers,  o.ooi  mfd. 

1  Gridleak  mounting 

2  Bypass  condensers  with  leads,  o.  i  mfd. 

3  Filter  condensers  with  leads,  4.0  mfd. 
i  looo-ohm  fixed  resistor 

i  25OO-ohm  fixed  resistor 

i  5000-ohm  fixed  resistor 

i  io,ooo-ohm  fixed  resistor 

3  6o-ohm  center-tapped  resistors 

It  is  also  a  good  idea  to  have  on  hand  a  half 
dozen  or  so  three-foot  lengths  of  flexible  wire 
with  clips  on  the  ends.  The  above  parts  arranged 
for  instant  clip  connections,  will  be  more  than 
handy  in  all  experimental  work. 

HERBERT  GRAHAM,  Chicago,   Illinois 

Volume  Control  for  Resistance- 
Coupled  Amplifiers 

COME  receivers,  particularly  sets  using  a.c. 
^  tubes,  employ  a  type  of  volume  control  such 
that  the  signal  cannot  be  reduced  without  im- 
pairing selectivity  to  a  serious  extent.  This  con- 
sideration justifies  the  control  of  volume  at  a 
point  in  the  circuit  following  the  detector  tube 
where  it  will  have  no  effect  on  selectivity.  Some 
circuits  employ  a  high  resistance  potentiometer 
across  the  secondary  of  the  first  audio  transfor- 
mer in  a  transformer-coupled  amplifier. 

When  using  a  resistance-coupled  amplifier  a 
somewhat  similar  arrangement  can  be  used,  and 
is  suggested  in  Fig.  3.  The  coupling  resistor  in 
the  detector  plate  circuit  is  a  high  range  potentio- 
meter (.1  to  .25  megohms  maximum)  such  as  the 
Electrad  Royalty,  with  the  movable  arm  con- 
nected to  the  coupling  condenser. 

This  arrangement  provides  adequate  volume 
control  without  changing  the  frequency  charac- 
teristic of  the  amplifier. 

H.  F.  KUCKS,  New  York  City. 

STAFF    COMMENT 

A  S  MR.  KUCKS  points  out  there  are  certain 
**  types  of  volume  controls  which  impair  the 
selectivity,  as  for  example  a  variable  resistance 
across  the  primary  or  secondary  of  an  r.  f.  trans- 
former. Such  difficulties  can  be  prevented  by 


FIG.    3 

A  volume  control  circuit  for  use 
with  resistance-coupled  amplifiers 


90 


•RADIO  BROADCAST 


JUNE,  1928 


placing  the  volume  control  in  the  audio  amplifier 
but  this  control  has  the  disadvantage  that  it  will 
not  prevent  the  detector  overloading  on  strong 
signals.  There  are  several  satisfactory  volume 
controls  that  can  be  applied  to  a.c.  receivers 
which  will  not  affect  the  selectivity  and  which 
will  also  prevent  detector  overloading  on  strong 
signals.  We  mention  two  types. 

One  fairly  good  control  is  a  variable  resistance 
connected  in  series  with  the  B-plus  lead  to  the 
primaries  of  the  r.  f.  transformers.  This  resistance 
should  have  a  maximum  value  of  about  200,000 
ohms  and  a  o.i-mfd.  or  larger  bypass  condenser 
should  be  connected  across  it.  As  the  amount  of 
resistance  in  the  circuit  is  increased,  the  effective 
voltage  applied  to  the  plates  of  the  r.  f.  is  lowered 
and  the  volume  is  thereby  decreased.  Such  a 
control  will  not  impair  the  selectivity,  but,  with 
some  receivers  will  cause  an  undesirable  in- 
crease in  voltage  applied  to  the  other  tubes 
in  the  set. 

A  simple  type  of  volume  control  that  may 
generally  be  used  merely  consists  of  a  variable 
resistance  connected  between  the  antenna  and 
ground  posts  on  the  set.  The  resistance  should 
have  a  maximum  value  of  about  50,000  ohms. 
Centralab,  Yaxley,  and  others  make  a  special 
resistance  for  this  purpose. 

Some   Baffle   Board   Experiments 

STAFF   COMMENT 

THE  baffle  board  consists  of  a  reflecting  sur- 
face applied  near  a  cone  speaker.  In  many 
cases  this  takes  the  form  of  a  large  box,  in  which 
the  cone  is  placed.  In  others  it  is  a  short  horn 
having  a  relatively  large  bell,  the  cone  being 
used  as  a  diaphragm.  In  many  instances,  the 
use  of  baffle  boards  will  improve  reproduction  of 
the  low  frequencies  especially.  As  experimental 
boards  are  easily  constructed,  they  are  worth 
trying. 

The  two  following  contributions  consider  the 
possibilities  of  the  use  of  baffles. 


FIG.   4 
A  baffle  arrangement  with  a  540  AW  cone  speaker 


0.00025 
mid. 


FIG.    5 

An  antenna  tuning  circuit  for  use  with  neutro- 

dynes  and  other  receivers  having  an  untuned 

primary  circuit 

IN  EXPERIMENTING  with  a  Western  Elec- 
*  trie  540  AW  cone  I  found  it  possible  to  attain 
a  marked  improvement  in  the  reproduction  of 
the  lower  audio  frequencies,  without  apparent 
impairment  of  the  higher  notes  through  the  use 
of  a  baffle  board.  The  accompanying  photograph, 
Fig.  4,  illustrates  the  baffle  arrangement  em- 
ployed by  the  writer. 

I  made  a  36  by  36-inch  wood  frame,  12  inches 
deep.  The  front  was  faced  with  heavy  roofing 
paper,  with  a  circular  hole,  eighteen  inches  in 
diameter,  cut  out  in  the  center.  The  cone  was 
placed  in  this  cabinet  with  the  face  of  the  cone 
brought  as  close  to  the  opening  as  the  frame  of 
the  loud  speaker  would  permit.  The  assembly 
was  then  mounted  on  top  of  the  chest  of  drawers 
as  shown  in  the  photograph,  and  placed  in  the 
corner  of  the  room  so  that  the  sides  of  the  en- 
closing cabinet  touched  the  walls.  By  so  doing 
the  baffle  effect  of  the  sides  was  greatly  increased, 
and  the  supporting  furniture  also  functioned  as 
part  of  the  baffle. 

The  power  tube  used  is  a  ux-iyi  outputting 
to  the  speaker  through  a  loo-henry  choke  coil 
and  a  g.o-mfd.  condenser.  This  tube  outputs  ade- 
quate distortionless  power  to  the  baffled  loud 
speaker  with  135  volts  on  the  plate. 

A  slight  barrel  effect  in 
speech  was  counteracted  by 
placing  a  piece  of  heavy  cloth 
on  the  back  of  the  cabinet, 
thus  avoiding  sound  reflec- 
tion. 

PAUL  S.  FOSTER,  New 
York  City. 


A  CAREFUL  considera- 
•"  tion  of  the  most  effective 
method  of  mounting  a  free- 
edge  baffle  type  cone  speaker 
is  necessary  if  the  best  results 
are  to  be  secured.  Fairly  good 
results  can  be  expected  by 
using  a  flat  baffleboard  of 
sufficient  thickness  and  rigid- 
ity to  be  nonresonant 
throughout  the  audio  range. 
A  deep  cabinet  or  console, 
however,  will  tend  to  improve 
the  lower  frequency  response 
of  the  speaker  by  allowing  a 
greater  effective  baffling  area. 
The  greater  the  baffling 
area  the  better  will  be  the 
reproduction  of  the  low 
notes. 

Deep  box  baffles  of  the 
type  to  which  we  have  refer- 
ence often  give  rise  to  a 
resonance  effect  within  the 
audio  range,  resulting  in  the 
exaggeration  of  certain  fre- 
quencies, noticeable  as  a 


booming  sound  or  barrel  tone.  One  method  of 
correcting  this  condition  is  to  vent  the  baffle 
by  cutting  holes  or  louvres  in  the  sides  of  the 
console.  This  has  the  disadvantage  of  reducing 
"  the  effective  baffling  area  and  often  impairs  the 
appearance  of  what  otherwise  would  be  a  hand- 
some bit  of  furniture.  At  best  my  present  sugges- 
tion is  a  trial  and  error  method. 

In  mounting  a  free-edge  cone  in  a  baffling 
arrangement  of  this  type,  the  writer  finds  that 
resonance  can  be  completely  eliminated  by  lining 
the  interior  with  felt.  Felt  packing  of  a  thickness 
of  j  inch  was  used,  although  a  somewhat  thinner 
lining  would  probably  have  worked  just  as  well. 
The  entire  interior  of  the  cabinet,  was  lined  with 
the  packing  and  secured  by  glue  and  tacks. 
D.  C.  REDGRAVE,  Norfolk,  Virginia. 

Antenna  Tuning  Device 

T^HE  apparatus  described  below-  is  an  indis- 
*  pensable  portion  of  my  receiver  equipment  for 
distant  reception.  Many  broadcast  fans,  located 
like  myself  at  some  distance  from  broadcast 
centers,  will  find  this  simple  device  of  use  to 
them. 

On  many  evenings,  when  stations  two  hundred 
to  three  hundred  miles  away  are  practically  in- 
audible, a  variometer  and  two  variable  conden- 
sers, connected  as  shown  in  Fig.  5  boost  the  vol- 
ume from  ten  to  twenty  times,  often  making 
enjoyable  loud  speaker  reception  possible.  The 
device  does  not  change  the  original  dial  settings 
of  the  receiver.  Once  the  variable  condensers  are 
set  to  the  proper  capacity  (to  be  determined  ex- 
perimentally) they  need  not  be  touched  again, 
all  tuning  being  effected  on  the  variometer. 
However,  the  o.ooo25-mfd.  variable  is  very 
effective  as  a  volume  control.  This  apparatus  is 
not  effective  on  all  receivers,  but  is  designed 
primarily  for  use  with  sets  having  untuned  an- 
tenna primaries,  such  as  the  average  neutrodyne 
and  tuned  r.f.  receiver. 

A.  GAUDETTE,  Lewiston,  Indiana. 

STAFF   COMMENT 

*~pHE  arrangement  described  -above  is  an  an- 
*•  tenna  tuning  device.  The  control  described 
by  Mr.  Gaudette  is  really  a  combined  antenna 
tuning  device  and  a  wave  trap.  In  the  majority 
of  instances  it  can  be  simplified  to  the  circuit 
shown  in  Fig.  6.  Coil  L  may  be  the  secondary 
of  any  available  radio-frequency  amplifying 
transformer,  or  sixty  turns  of  wire  wound  on  a 
three-inch  diameter  form.  This  device  will  be 
most  effective  on  short  indoor  antennas. 

A  Spark  Plug  Lightning  Arrester 

j_I  ERE  is  a  simple  and  effective  lightning  ar- 
'   rester.   It  consists  of  a  good  heavy   spark 
plug,  and  a  piece  of  pipe,  three  or  four  feet  long, 
into  which  the  plug  can  be  screwed. 

The  pipe  is  driven  into  the  ground  and  the 
spark  plug  screwed  into  it.  The  ground  connec- 
tion is  automatically  taken  care  of.  The  wire 
from  the  antenna  is  led  to  the  binding  post  on 
top  of  the  spark  plug  and  from  there  to  the  re- 
ceiver. That  is  all  there  is  to  it. 
GEORGE  KOETHER,  JR.,  Round  Bay,  Maryland. 


\ 

7 

Hi 

/ 

k     To  Ant  Post 
<O<         on  Set 

•1 

0.0005 

§j                   FIG.    6 

mfd.         . 

CZX    A  simplified  version  of 

• 

<O\    Fig.  5.  Both  Fig.  5  and 

<^j    Fig.  6  are  most  effec- 

S    five  when   used   with 

short  antennas 

JUNE,  1928 


RADIO  BROADCAST 


91 


No.  1. 


June,  1928. 


RADIO  BROADCAST'S  Service  Data  Sheets  on  Manufactured  Receivers 


The  Amrad  A.  C.  7 


THE  Amrad  A.  C.  7  is  another  representative 
of  the  a.c.  electric  receiver  of  the  neutrodyne 
type.  This  receiver  utilizes  seven  tubes,  six 
of  which  are  of  the  a.c,  type  while  the  seventh  is  a 
171.  A  study  of  the  wiring  diagram  of  the  complete 
receiver  installation  will  bring  to  light  several  novel 
features  in  design.  There  are  four  stages  of  radio- 
frequency  amplification,  a  non-regenerative  de- 
tector, and  two  stages  of  transformer-coupled  audio- 
frequency amplification.  The  power  is  obtained 
from  a  full-wave  B  power  unit  which  simultane- 
ously supplies  the  B  voltage  for  the  plates  of  the 
tubes  and  the  a.c.  voltages  for  the  filaments. 

The  r.f.  system  consists  of  an  antenna  coupling 
stage  and  three  stages  of  Hazeltine-neutralized 
tuned  radio- frequency  amplification.  The  receiver 
is  designed  for  a  short  antenna  and  the  first  r.f. 
stage  is  really  a  coupling  stage,  being  untuned.  The 
input  circuit  of  this  coupling  tube  consists  of  a 
radio- frequency  choke,  tapped  for  the  antenna,  in 
series  with  a  fixed  resistance,  which  is  grounded. 
By  utilizing  this  coupling  tube  the  tuned  settings 
of  the  other  three  stages  are  not  disturbed  by 
variations  in  antenna  length  or  capacity.  A  very 
novel  method  of  volume  control  for  the  entire  re- 
ceiver installation  is  incorporated  in  the  plate  cir- 
cuit of  this  coupling  tube.  It  consists  of  a  variable 
•  resistance  connected  across  the  bifilar  primary 
winding.  Under  normal  circumstances  a  volume- 
control  of  this  type  would  manifest  an  effect  upon 
the  grid  circuit  of  the  average  tuned  stage  but  since 
the  grid  circuit  of  this  tube  is  untuned  the  effect 
of  this  variable  resistance  is  that  of  only  a  volume 
control,  without  any  detrimental  effects  upon  other 
circuits.  Each  of  the  r.f.  stages  is  contained  in  a 
separate  can.  The  audio  stages  are  not  shielded  and 
are  of  the  conventional  type,  with  an  output  trans- 
former utilized  to  couple  the  loud  speaker  to  the 
output  tube. 

All  four  stages  of  radio-frequency  amplification 
are  neutralized,  and  the  neutralizing  condensers 
are  designated  as  C?  in  the  wiring  diagram.  The 
bifilar  primaries  utilized  in  this  system  of  neutrali- 


Coupling Tube        1st  R.F 

" 


zation  are  marked  Li  in  the  drawing.  The'receiver 
is  a  single-control  unit,  the  four  tuning  condensers 
being  ganged  together  and  operated  from  one  point. 
A  filter  system,  consisting  of  a  resistance  and  a 
capacity,  is  incorporated  into  the  detector  plate 
circuit,  probably  to  keep  the  a.c.  hum  at  a  low 
value.  The  plate  voltages  for  the  r.f.  tubes  and 
the  detector  are  obtained  from  one  tap  on  the 
power  unit,  but  voltage-reducing  resistances  lo- 
cated in  the  plate  circuit  of  each  radio-frequency 


THE  SET  IN  ITS  CABINET 


tube  and  in  the  plate  circuit  of  the  detector  tube, 
reduce  this  voltage  to  the  correct  values  for  the 
individual  tubes.  It  should  be  understood  that 
volume  control  in  this  installation  is  not  accom- 
plished by  plate-voltage  reduction.  At  first  glance 
one  would  assume  this  to  be  the  case.  Volume- 
control  is  obtained  by  a  resistance  which  varies 
the  a  .c .  yol  tage  across  the  first-radio-frequency 
primary  winding.  Bypass  condensers  are  used  to  by- 
pass the  filament  and  plate  circuit  in  every  stage: 
to  further  facilitate  receiver  stability,  a  radio- 


frequency  choke  is  wired  into  the  plate-voltage 
system  in  the  r.f.  circuit. 

As  was  stated,  the  filament  circuits  are  all  a.c.; 
and  electrical  balance  is  obtained  by  means  of  po- 
tentiometers. These  are  designated  as  Pi,  P2l  and 
Ps  in  the  wiring  diagram.  The  grid  bias  for  the  vari- 
ous -tubes  is  obtained  by  means  of  a  resistance 
through  which  the  plate  current  flows  and  results 
in  a  predetermined  voltage  drop.  These  voltage- 
drop  resistances  are  marked  Rj  and  RB.  As  is  evi- 
dent from  the  drawing,  the  grid  bias  voltage  is  of 
like  value  for  the  r.fT  and  the  first  audio  tube, 
while  individual  grid  bias  is  obtained  for  the  out- 
put tube. 

The  power  unit  is  of  conventional  type  with  two- 
variations.  The  rectifying  tube  is  of  the  280  full- 
wave  type.  As  a  contrast  to  other  filter  systems  em- 
ployed in  rectifiers,  this  installation  utilizes  but  one 
filter  choke.  The  required  filtering  action  is  ob- 
tained by  the  use  of  large  values  of  capacity.  A 
Mershqn  condenser  of  several  sections  (each  sec- 
tion being  of  relatively  high  capacity)  is  employed. 
As  is  evident  in  the  wiring  diagram,  two  sections  of 
this  condenser  are  connected  across  taps  of  the 
voltage  distributing  resistance.  This  aids  materi- 
ally in  the  lowering  of  the  effective  resistance  of  the 
output  circuit,  and  in  the  reduction  of  regenera- 
tion due  to  the  action  of  this  resistance  as  an  im- 
pedance common  to  all  circuits.  The  power  trans- 
former utilized  consists  of  six  windings.  The  pri- 
mary winding  is  tapped  for  three  values  of  line 
voltage.  One  secondary  winding  supplies  the  fila- 
ment voltage  for  the  rectifying  tube,  another 
supplies  the  plate  voltage  for  this  tube.  The  other 
three  supply  the  a.c.  filament  voltages  necessary 
for  the  various  tubes  in  the  receiver.  Since  a  shunt 
potentiometer  method  of  obtaining  electrical  bal- 
ance is  utilized,  center  taps  on  the  a.c.  filament 
windings  are  unnecessary.  Control  of  the  complete 
receiver  is  accomplished  by  means  of  a  switch  in 
series  with  the  house  supply  circuit  and  the  trans- 
former primary.  This  switch  is  located  on  the  face 
of  the  receiver  panel. 


2.5  Volts    White 

*v^~v'~V — V 
^X^^A— *^_ •*•  __ 

k&  Yellow  5  Volts 

THE  CIRCUIT  DIAGRAM  OF  THE  AMRAD  A.  C.  7 


92 


RADIO  BROADCAST 


JUNE,  1928 


No.  2. 


June,  1928. 


RADIO  BROADCAST'S  Service  Data  Sheets  on  Manufactured  Receivers 


The  Pfansteihl  A.  C.  34  and  50 


CIMPLICITY  of  design  marks  the  develop- 
"  ment  of  the  PfanstieW  line  of  radio  receivers. 
The  photograph  and  wiring  diagram  shown  here- 
with apply  to  both  the  Nos.  34  and  50  a.c.  electric 
receivers.  The  34  is  the  console  model,  whereas 
the  50  is  the  table  model  of  the  same  receiver. 

This  receiving  system  employs  6  tubes,  appor- 
tioned as  three  stages  of  tuned  radio-frequency  am- 
plification, non-regenerative  detector,  and  two 
stages  of  transformer-coupled  audio  amplification. 
The  wiring  diagram  of  the  system  is  shown  here- 
with. As  is  evident  from  the  drawing,  226  type  a.c. 
tubes  are  used  for  the  three  radio-frequency  ampli- 
fiers and  for  the  first  stage  of  audio.  A  227  type  de- 
tector is  employed  and  a  171  is  the  output  audio 
tube,  arranged  in  conventional  transformer-coupled 
fashion.  The  four  226's  are  wired  in  parallel  and  ob- 
tain their  filament  potential  from 
a  1.5-volt  winding  on  the  power 
transformer.  The  tuning  system 
used  in  the  tuned  radio-frequency 
stages  is  conventional,  consisting 
of  fixed  inductances  and  variable 
capacities.  The  method  of  stabili- 
zation employed  makes  use  of  grid 
resistances,  commonly  known  as 
grid  "suppressors." 

In  order  to  attain  utmost  sim- 
plicity, only  two  values  of  plate 
voltage  are  applied  to  the  receiver. 
The  three-radw>frequency  stages 
and  the  two  audio-frequency  tubes 
obtain  their  plate  voltage  from  the 
same  voltage  tap,  while  there  is 
another  tap  for  the  detector.  The 
first  radio-frequency  tube's  plate 
voltage  is  governed  by  a  potenti- 
ometer type  of  resistance  which 
shunts  the  plate  coil  of  the  first 
radio-frequency  tube.  The  standard 
grid-leak  condenser  system  of  de- 
tection is  employed. 

The  audio  system  is  conventional 
in  every  way.  The  volume  control 
is  a  voltage  divider  shunting  the 
secondary  of  the  first  audio- 
frequency transformer,  with  the 
center  tap  of  this  control  connected 
to  the  grid  of  the  amplifying  tube. 


THE  RECEIVER  WITH   ITS  POWER  UNIT 


The  secondary  of  the  second  audio-frequency  trans- 
former is  shunted  with  a  fixed  capacity.  The  C  bias 
for  the  output  audio  tube  is  obtained  by  causing  a 
voltage  drop  across  a  resistance  in  the  grid  return 
lead. 

The  receiver  is  divided  into  two  parts,  the  radio 
and  audio  systems  being  contained  in  one  can,  while 
the  power  unit  is  in  another  can.  The  wiring  sys- 
tem employed  in  the  power  unit  is  standard.  Two 
transformers  are  employed.  One  is  the  power  trans- 
former supplying  the  filament  and  plate  voltages 
required  for  the  full-wave  filament  type  rectifying 
tube,  and  the  other  is  the  filament  transformer  sup- 
plying the  1.5  -,  2.5-,  and  5-volt  windings  for  the 
tube  filaments.  The  primaries  of  these  two  trans- 
formers are  connected  in  parallel  and  are  designed 
for  a  115-volt  a.c.  line.  The  filament  windings 
supplying  the  1 .5  and  the  2.5.  volt- 
ages are  equipped  with  voltage  C9n- 
trol  resistances  thus  safeguarding 
the  tube  filaments  in  the  event  of 
an  excessive  line  surge  or  increase 
in  line  voltage.  The  (filter  system 
consists  of  a  two-section  filter,  with 
a  single  distributing  resistance 
across  the  output.  The  "high"  side 
of  this  resistance  supplies  the  plate 
voltage  for  all  tubes  other  than  the 
detector  tube.  A  tap  supplies  the 
detector  plate  voltage. 

The  electrical  balance  and  the 
electrostatic  balance  in  the  filament 
circuit  is  obtained  by  means  of  mid- 
tapped  resistances  placed  in  parallel 
with  the  tube  systems,  rather  than 
by  tapping  the  filament  voltage 
winding. 

The  loud  speaker  coupling  to 
the  output  audio  tube  is  direct, 
without  any  transformer  or  choke- 
condenser  system.  Two  output 
binding  posts  are  provided  for  the 
loud  speaker  terminals.  If  desired, 
a  loud  speaker  coupling  unit  can 
be  added  to  the  receiver. 

Tuning  is  accomplished  by 
means  of  single-dial  control,  the 
second  knob  on  the  front  panel 
being  for  volume  control. 


THE    PFANSTEIHL   MODEL    50   A.C.    RECEIVER 


\T7Ant 


r  Gnd. 


CIRCUIT   OF    THE    PFANSTEIHL    MODELS    34    AND    50.    THE    POWER    UNIT    IS    SEPARATE 


Building  and  Operating  the  A.  C.  "R.  B.  Lab"  Receiver 

By  Hugh  S.  Knowles 


HOW  THE 


A.C.  LAB  RECEIVER  LOOKS—  BEHIND  THE  PA^EL 


IF  THE  experience  of  those  who  manufacture 
both  battery  and  a.c.  operated  receivers  is 
any  criterion  there  is  no  question  about  the 
present  being  an  "all  electric"  season.  This  de- 
mand for  a.c.  receivers  has  been  reflected  in  the 
custom  set-building  field  where  experimenters 
are  looking  askance  at  any  circuit  which  cannot 
be  modified  to  permit  operation  from  the  lighting 
circuit. 

The  use  of  a.c.  tubes  does  not  alter  the  funda- 
mental operation  of  a  circuit  and  for  this  reason 
it  is  quite  natural  to  look  for  receivers  using  well- 
known  and  tried  circuits  which  have  been  modi- 
fied slightly  to  make  the  use  of  these  tubes  possi- 
ble. 

In  this  connection  the  receiver  we  are  about 
to  describe  should  be  of  particular  interest  to  the 
readers  of  RADIO  BROADCAST.  It  uses  the  familiar 
R.  B.  Lab  circuit,  with  its  possibilities  for  ex- 
cellent performance  with  a  minimum  number 
of  tubes  together  with  selected  parts  which  make 
possible  the  realization  of  this  performance. 

The  circuit  itself  needs  no  introduction,  since 
the  original  and  several  variations  have  appeared 
in  RADIO  BROADCAST.  Those  who  are  interested 
in  an  exposition  of  the  special  features  of  this 
circuit  are  referred  to  the  June,  1926,  and  April, 
1928,  issues.  The  principal  advantage  of  this  over 
other  similar  four-tube  arrangements  lies  in  its 
"gain"  or  sensitivity  and  in  the  fact  that  the 
balancing  circuit  of  the  Rice  type  gives  accurate 
neutralization  over  the  whole  frequency  range. 
The  grid  "suppressor"  or  losser  method  of 
stabilization  is  not  used  in  the  radio-frequency 
stage.  This  element  of  design  improves  the 
selectivity  of  this  circuit  and  makes  it  more 
uniformly  selective  over  the  whole  frequency 
range. 

The  advantages  of  a.c  operation  have  been 
obtained  together  with  an  actual  improvement 
in  performance,  due  to  the  fact  that  a.c.  tubes 
in  general  are  somewhat  better  amplifiers  than 
the  standard  201 -A  type.  Direct  comparative 


tests  between  this  receiver  and  one  of  the  battery 
types  indicates  an  improvement  in  gain  or  sensi- 
tivity, better  stability  and  negligible  hum  or  a.c. 
modulation  even  on  the  more  distant  stations. 

One  addition  has  been  made  to  the  circuit;  a 
dummy  socket  has  been  connected  in  parallel 
with  the  detector  socket.  This  makes  it  possible 
to  plug-in  a  phonograph  pick-up  permanently. 
The  small  switch  between  the  drum  dials  permits 
an  instantaneous  change  from  receiver  to  pick-up. 
This  convenience  will  be  appreciated  by  those 
who  have  had  to  open  the  cabinet,  remove  the 
detector  tube,  plug-in  the  pick-up  and  then 
perform  the  inverse  operation  to  operate  the 
receiver  again. 

An  inspection  of  the  schematic  wiring  diagram 
in  Fig.  2  will  show  that  two  minor  changes  have 
been  made  in  the  radio-frequency  circuits.  The 
resistance  R2  has  been  substituted  for  the  radio- 
frequency  choke  previously  used  in  the  mid-tap 
of  the  first  coil,  and  the  condenser  C3  has  been 
added. 

The  resistance  prevents  very  high  frequency 
oscillations  which  would  block  the  first  tube. 
For  this  purpose  it  is  just  as  satisfactory  as  the 
choke  and  less  expensive.  This  resistance  is  not 


CT"HE  set  described  here  is  a  straight  four-tube 
•*•  "Lab"  circuit  receiver,  arranged  to  operate 
entirely  from  the  a.c.  line.  The  results  achieved  are 
rather  better  than  tbose  from  the  average  four- 
tube  set,  due  to  the  high  gain  in  the  radio  fre- 
quency circuit.  Mr.  Knowles'  receiver  is  a  well 
arranged  set  based  on  exactly  the  same  circuit, 
with  the  exception  of  provision  for  a.c.  operation 
for  the  filaments,  that  was  described  on  page  423 
in  ibis  magazine  for  April,  1928.  That  unusually 
interesting  story  dealt  with  the  engineering  design 
which  went  into  this  receiver  and  exact  measure- 
ments of  its  performance. 

— THE  EDITOR. 


93 


in  any  sense  a  "grid  suppressor"  at  broadcast 
frequencies  since  a  high-impedance  choke  may 
be  used,  or  the  circuit  left  open,  for  that  matter. 
In  practice  the  mid-tap  connection  is  used  to 
provide  a  means  of  biasing  the  first  tube. 

THE  CIRCUIT 

T^HE  principal  circuit  modifications  are  those 
*  made  necessary  by  the  a.c.  tubes.  Three 
227  type  tubes  are  used  and  a  lyi-A  type  in  the 
last  audio-frequency  stage.  Heater  type  tubes 
have  been  used  in  the  radio-frequency,  detector, 
and  first  audio-frequency  stages  because  of  their 
comparative  freedom  from  hum  or  ripple.  Tubes 
of  the  raw  a.c.  type  may  be  adjusted  to  give  very 
little  hum  but  any  change  in  the  effective  plate 
voltage  increases  the  a.c.  modulation  consider- 
ably. 

The  filament  current  for  the  tubes  is  supplied 
by  a  step-down  transformer  T8.  To  insure  long 
heater  life,  care  should  be  taken  to  see  that  this 
transformer  is  one  of  the  new  types  designed  to 
give  2.25  volts.  The  old  type  supplies  2.5  volts. 

Bias  for  the  radio-frequency  and  first  audio- 
frequency circuits  is  secured  by  taking  the  drop 
across  a  resistor  in  the  plate  circuit  of  the  tubes. 
This  method  is  quite  satisfactory  where  a  single 
stage  of  radio-frequency  amplification  is  used. 

No  B  socket-power  device  has  been  used  in 
the  receiver  since  it  was  felt  that  many  con- 
structors would  have  ones  which  were  previously 
used  with  battery-type  receivers  and  others 
would  have  power  amplifiers  in  which  such  a  B- 
power  supply  was  included.  Where  this  is  not 
the  case  any  good  quality  power  unit  may  be 
used  and  the  receiver  made  "all  electric." 

In  most  cases  it  is  advisable  to  use  a  C  battery 
for  the  power  tube.  There  is  really  little  or  no 
objection  to  this  practice  since  the  life  of  the  C 
battery  is  determined  by  its  "shelf  life"  which 
may  be  in  excess  of  a  year.  Details  for  avoiding 
the  use  of  this  battery  will  be  given  later.  (See 
Fig.  i). 


94 


RADIO  BROADCAST 


JUNE,  1928 


THE    LAB    SET   IN    ITS   CABINET 


Special  coils  are  available  for  this  circuit  and 
receiver  which  require  no  alterations.  Any  of 
the  coils  designed  for  a  o.oooj-mfd.  condenser 
may  be  used  however.  The  Aero  1)95  set  has  two 
coils  and  will  be  discussed  as  a  convenient  and 
typical  set  which  may  be  modified. 

REVAMPING    STANDARD   COILS 

REMOVE  the  hinged  primary  winding  from 
the  antenna  coil  leaving  nothing  but  the 
main  secondary  winding  connected  to  terminals 
I  and  6.  Remove  the  primary  from  the  detector 
coil  by  carefully  breaking  the  bakelite  tubing  on 
the  inside  and  unsoldering  the  leads  going  to 
terminals  2,  3,  4  and  5. 

Tap  one  of  the  coils  at  the  center  turn  verti- 
cally above  terminal  No.  I.  Tap  the  other  coil 
one  third  of  the  way  up  from  the  bottom  verti- 
cally over  terminal  No.  2.  Wind  a  thin  strip  of 
insulating  material  such  as  thin  celluloid  or 
varnished  cambric  about  half  an  inch  wide  over 
the  center  of  the  mid-tapped  coil.  Pierce  a  small 
hole  in  the  insulation  and  bring  out  the  center- 
tapped  strip  through  it.  Wind  eight  turns  of 
wire  (No.  28  d.c.c.  is  all  right,  but  the  size  is 
electrically  not  at  all  important)  on  each  side 
of  the  midtap  for  the  primary.  Anchor  the  two 
end  turns  by  looping  them  under  the  vertical 
bakelite  coil  support. 

The  baseboard  and  panel  should  be  prepared 
in  the  usual  manner.  The  template  drawing, 
packed  with  the  drum  dials  may  be  used  as  a 
drilling  template. 


Because  of  the  height  of  the  drum  dials,  the 
condensers,  d  and  Cj,  must  be  mounted  on 
"stilts"  or  bushings.  In  this  case  two  pieces  of 
brass  tubing  cut  to  the  proper  length  were  used. 
As  the  condensers  are  mounted  in  this  receiver, 
the  reading  of  the  drums  increases  with  wave- 
length. If  the  readings  are  to  increase  with  fre- 
quency the  condensers  should  be  reversed.  The 
full  floating  shafts  make  this  possible.  This 
feature  also  permits  bakelite  or  hardwood  shafts 
to  be  substituted.  These  will  be  discussed  under 
the  operating  details. 

The  location  of  the  parts  is  very  important. 
In  experimenting  with  the  layout,  for  example, 
it  was  found  that  moving  the  choke,  (L<),  over 
between  the  drum  dials  made  the  set  unstable. 
This  trouble  was  found  to  be  due  to  the  greater 
length  of  the  "hot"  plate  lead  and  not  to  cou- 
pling between  the  choke  and  coil  as  might  have 
been  supposed.  A  discussion  of  the  important 
leads  to  watch  appeared  in  the  June,  1926,  RADIO 
BROADCAST  under  the  title  "Additional  Notes  on 
the  R.  B.  Lab  Circuit." 

There  is  nothing  "tricky"  about  the  wiring. 
All  a.c.  filament  leads  should  be  twisted.  Bus 
bar  wiring  was  used  in  this  set  so  the  connections 
could  be  easily  traced  in  the  photographs.  All 
the  battery  leads  may  be  cabled  if  flexible  wire 
is  used.  There  is  no  objection  to  using  "bee" 
line  or  direct  point  to  point  wiring  if  the  leads 
are  carefully  spaced.  For  details  on  the  arrange- 
ment of  the  leads  see  the  photographs  and 
Fig-  3- 


The  two  A-battery  leads  on  the  cable  are  not 
used.  If  an  outside  C  battery  is  to  be  used  for 
the  radio-frequency  and  first  audio-frequency 
stages  it  may  be  added  by  making  the  following 
changes:  Remove  Rs  and  Cj  and  connect  the 
leads  going  to  the  K  terminals  on  the  227  sockets 
to  the  minus  B  or  yellow  cable  terminal.  Connect 
the  lead  going  to  the  minus  C  terminal  of  the 
first  audio-frequency  transformer  and  the  one 
connected  to  R%  to  the  black  cable  terminal. 
Connect  C?  across  the  black  and  yellow  cable 
terminals.  The  C  battery  is  then  connected 
externally  by  using  the  yellow  and  black 
leads  as  the  positive  and  negative  leads  re- 
spectively. 

WHEN    A    B-POWER    UNIT    IS    USED 

I F  B-power  unit  which  supplies  180  volts  is 
'  used,  a  C  battery  with  proper  potential  for 
the  tube  employed  should  be  used  for  the  power 
tube.  Where  the  power  device  supplies  200  volts 
or  more,  an  arrangement  such  as  indicated  in  Fig. 
I  may  be  used.  A  jo-henry  choke  and  2.0-  or  4.0- 
mfd.  condenser  should  be  used  to  keep  the  direct 
current  out  of  the  speaker.  When  the  speaker 
return  is  connected  as  shown,  the  2ooo-ohm  grid 
biasing  resistor  is  not  in  the  return  circuit  and 
this  insures  better  reproduction  of  the  lower 
audio  frequencies. 

No  output  device  is  used  in  the  receiver.  This 
reduces  the  cost  of  the  parts  when  a  I12-A  type 
tube  is  used  or  a  lyi-A  type  with  only  135  volts 
on  the  plate.  If  an  external  power  amplifier  is  to 


r|G<ay 
Q | 


B-         Del             Int. 

B  SocXet-Powei 
Unit 

Power 

AN    UNUSUALLY    EFFICIENT    SET   IN    SMALL    SPACE 


FIG.    I 


be  used  the  last  audio-frequency  transformer  may 
be  omitted.  In  some  cases  the  power  amplifier 
includes  an  audio  stage  ahead  of  the  power  tube 
and  in  this  case  the  detector  output  may  be  con- 
nected directly  to  the  speaker  jacks  on  the  cable 
terminal. 

The  dial  lights  should  be  connected  in  parallel 
across  the  filament  of  the  lyi-A  tube. 

Very  little  adjustment  should  be  necessary 
after  the  receiver  is  completed.  In  adjusting  the 
balancing  circuit  the  "dead  filament"  method  is 
not  very  desirable  nor  convenient  in  this  case. 
Tune-in  a  carrier  in  the  short-wave  section  of 
the  broadcast  band  and  set  the  detector  regenera- 
tion control  so  the  set  just  oscillates.  Use  a  screw 
driver  made  from  a  bakelite  or  fiber  strip  to  ad- 
just the  balancing  condenser.  Tune  the  radio- 
frequency  stage  first  to  one  side  of  the  carrier  and 
then  to  the  other  slowly  while  adjusting  the 
"equalizer." 


JUNE,  1928        BUILDING  AND  OPERATING  THE  A.  C.  "R.  B.  LAB"  RECEIVER 


95 


constructor  prefers  to  make  his  own  coils,  are  in- 
dicated on  the  diagram,  Fig.  2. 

PARTS  LIST 

Li,  L,  Aero  Products  Co.,  (i)  Pr.  U-95, 
or  Special  Lab.  Coils  .  ... 

Ci,  Cj  Hammarlund,  (2)  ML-2J  Con- 
densers    .  . 

G  Hammarlund,  (O-MC-ij  Midget    . 

U  Hammarlund  (i)  RFC-S;  Choke     . 

C*  Hammarlund,  (i)  Equalizer 

Micarta  (Westinghouse  Co.),  (i)  7"  x 
21"  x|"  Black  Panel  .  .  . 

Ri  Electrad  (i)  Type  P  Volume  Control 

R2,  R3  Electrad  (2)  joo-Ohm  Grid  Type 
Resistors 

Re  Electrad,  (i)  V-jo  Resistance    .     . 

R<  Electrad,  (i)  V-io  Resistance     . 

Yaxley,  (i)  669  Cable 

Yaxley,  (i)  S.P.D.T.  Switch  No.  30     . 

Ti,  T2  Silver-Marshall,  (2)  240  Audio 
Transformers 

T3  Silver-Marshall,  (i)  247  Filament 
Transformer 


y,  (3)  5-Prong  Sockets 
y,  (2)  4-Prong  Sockets 


FIG.    2 


Eby, 

Eby,  (2)  Binding  Posts 

C;,  Cs  Tobe,  (2)  i.o-mfd.  Bypass  con- 

densers  ......... 

C»  Aerovox,  (i)  0.00025  Grid  Conden- 

ser    .......... 

R8  International  Resistance  Co.  (i)  2.0 

Meg.  Grid  Leak      ...... 

International  Resistance  Co.,  (i)  Leak 

Mount    ......... 

National  Co.,  (2)  Single  Drum  Dials   . 


$  8.00 
1 1 .00 

2.OO 
2.OO 

5° 

2.20 
1.50 

50 

•75 
•75 
3-25 
90 

12.00 

5.00 
1.50 
.80 
30 

i. 80 
.40 
.50 

.50 
9.00 


When  the  adjustment  is  properly  made  there 
will  be  a  slight  "swishing"  sound  as  the  r.f. 
circuit  is  tuned  to  the  station  and  the  signal  will 
clear  up.  If  the  detector  is  placed  on  the  point 
of  oscillation,  there  will  be  no  tendency  for  the 
r.f.  stage  to  make  it  oscillate  as  the  r.f.  dial  is 
turned.  It  may  be  necessary  to  readjust  the 
regeneration  control,  (Cs),  slightly  to  make  the 
balance  adjustment  more  exact  although  the 
setting  is  not  very  critical. 

After  the  set  is  balanced,  the  effect  of  hand- 
capacity  should  be  tried  on  a  weak  station.  If 
there  is  any  appreciable  effect,  a  bakelite  or 
hardwood  shaft  should  be  substituted  for  the 
brass  one  used  with  each  condenser.  The  effect 
may  be  further  reduced  after  this  change  has 
been  made  by  grounding  the  metal  frame  of  the 
dials. 

If  the  antenna  stage  tunes  broadly  it  is  an 
indication  that  the  antenna  is  too  large  and  the 
effective  capacity  should  be  reduced  by  connect- 
ing a  fixed  condenser  about  o.oooi-mfd.  capacity 
in  series  with  the  antenna  lead.  The  selectivity 
of  the  first  stage  should  be  measured  with  the 
volume  control  in  the  full  "on"  position  since 
this  resistance  reduces  the  selectivity.  When  the 
set  is  tuned  to  a  station  where  the  volume  control 
is  near  the  "off"  position,  the  question  of  selec- 
tivity is  never  important. 

Since  the  volume  control  is  in  the  radio- 
frequency  circuit,  special  provision  must  be 
made  for  controlling  the  volume  of  the  phono- 
graph pick-up  arrangement.  Nearly  all  of  the 
standard  pick-ups  with  which  we  are  familiar  are 
sold  with  a  special  volume  control. 

To  minimize  hum,  the  B-power  circuit  should 
be  grounded.  Usually  the  ground  works  most 
satisfactorily  on  the  minus  B  lead.  In  some  cases 
the  hum  is  reduced  by  grounding  the  plus  45-volt 
tap  which  in  this  set  connects  to  the  neater 
winding  mid-tap.  Only  one  of  these  leads  should 
be  grounded,  however. 

If  an  outdoor  antenna  is  not  available,  the 
experimenter  may  try  connecting  a  o.oo2-mfd. 
fixed  high  quality  mica  condenser  from  one  side 
of  the  house-lighting  circuit  to  the  antenna 
binding  post.  Both  sides  of  the  line  should  be 
tried  since  one  side  may  be  grounded.  In  this 


case  the  line  acts  as  the  collector  and  the  signal 
is  brought  to  the  receiver  much  as  it  is  in  carrier- 
current  telephony. 

The  list  of  parts  below  are  those  used  in  the 
model  described  here.  Other  parts,  electrically 
and  mechanically  similar,  may  of  course,  be 
used. 

The  coils  Lj  and  Ls  are  special  and  are  sup- 
plied by  Aero  Products.  If  the  builder  desires  to 
revamp  the  standard  Aero  coil  set,  No.  Ugs,  he 
should  follow  instructions  on  page  94.  The 
dimensions  for  all  the  coils,  in  the  event  the 


865.15 

ADDITIONAL   PARTS 

(Needed  to  complete  the  set  as  described), 
(i)  Phonograph  pick-up,  with  volume  control. 
(i)  B  Power-Unit,  furnishing  a  maximum  voltage 

of  220,  at  40  mils.,  with  taps  as  follows:  45, 

90,  180,  -40. 
(3)  a.  c.  227  type  tubes. 

(i)  Power  tube,  Type  1 12-A  or  I7I-A  (See  Text). 
(i)  C  Battery  (Optional,  see  text;  rating  depends 

on  power  tube  used), 
(i)    Corbett    cabinet    to    accommodate    panel 

(7x21  x|"). 


FIG.    3 


Using  the  Screen-Grid  Tube  in  Popular  Circuits 
By  THE  LABORATORY  STAFF 


M' 


"ANY  experimenters  have  written  the 
laboratory  for  information  to  enable 
them  to  use  a  screen-grid  tube  in  the 
r.f.  stage  of  such  circuits  as  the  R.  B.  Lab., 
Universal,  Aristocrat,  Browning-Drake,  and 
other  sets  consisting  essentially  of  a  stage  of 
radio-frequency  amplification  followed  by  a 
regeneratve  detector.  The  adaptation  of  this 
tube  to  the  latter  receiver  has  been  described  in 
the  May  RADIO  BROADCAST  and,  in  the  same  is- 
sue was  described  an  a.c.-operated  all-wave 
receiver  using  a  screen-grid  r.f.  stage  with  the 
tube  operated  with  a.c.  on  its  filament. 

There  were  no  special  problems  involved  in 
the  design  of  an  a.c.  Lab  set  using  a  type  227 
tube  in  the  r.f.  stage  and  the  construction  of 
such  a  receiver  was  completed  with  little  trouble; 
the  result  of  this  work  has  been  described  in  the 
preliminary  article  in  the  April  issue  and  in  the 
construction  article  appearing  in  this  issue. 
After  the  construction  of  the  a.c.  set  had  been 
completed,  experiments  were  made  to  deter- 
mine how  satisfactorily  the  type  222  could  be 
substituted  for  the  227  in  the  r.f.  stage. 

The  tests  described  here  have  been  confined 
to  the  "Lab"  receiver,  and  since  individual 
tests  on  the  various  receivers  mentioned  in  the 
first  paragraph  have  not  been  made  it  cannot 
be  stated  positively  that  the  tube  will  work 
equally  well  in  all  these  circuits.  However,  since 
they  are  all  essentially  the  same,  the  operation  of 
the  screen-grid  tube  as  an  r.f.  amplifier,  in  these 
various  sets,  shouldn't  differ  very  much. 

The  experiments  on  the  "Lab"  circuit  were 
begun  by  first  setting  up  the  receiver  for  opera- 
tion with  a  227  in  the  r.f.  stage.  A  modulated 
oscillator  (the  construction  of  which  was  de- 
scribed in  the  June,  1927,  issue)  was  located  about 
10  feet  away  and  its  output  cut  down  until  the 
signal  from  it  was  just  audible  in  the  output  of 
the  "Lab"  set.  The  227  was  then  removed  and 
the  circuit  rewired  for  the  screen-grid  tube  in 
place  of  the  type  227  tube  in  the  r.f.  stage  with 
the  filament  of  the  screen-grid  tube  operated 
from  a  storage  battery.  The  circuit  is  given  in 
Fig.  I.  The  plate  of  the  screen  grid  is  coupled, 
through  a  fixed  condenser,  C,  with  a  value  of 
o.oooi  mfd.  or  larger,  to  the  grid  end  of  the  coil 
in  the  detector  grid  circuit.  The  plate  voltage 
for  the  cx-322  is  obtained  through  the  r.f. 
choke.  Using  the  322  there  was  quite  a  defi- 
nite increase  in  the  output  of  the  "Lab"  re- 
ceiver. The  change  in  detector  plate  current — 
which  is  a  measure  of  the  signal  impressed  on  the 
grid  of  the  detector — was  too  small  to  measure 
when  the  227  was  used.  With  the  screen-grid 
tube,  the  change  in  plate  current  was  quite  no- 
ticeable indicating  a  definite  increase  in  gain 
due  to  the  screen-grid  tube.  This  circuit  has  the 
disadvantage  that  the  322  must  be  supplied  with 
filament  current  from  a  battery  source.  The  fila- 
ment of  a  322,  being  the  same  as  that  in  a  120 


type  tube,  requires  0.132  amperes  at  3.3  volts 
which  may  be  supplied  economically  from  three 
dry-cells  but  it  would,  of  course,  be  an  advantage 
if  the  filament  could  be  operated  by  a.c.  supplied 
by  the  filament  transformer  used  to  heat  the 
filaments  of  the  tubes  in  the  circuit. 

The  next  step,  therefore,  was  to  rewire  the 
"Lab"  circuit  for  a.c.  operation  of  the  cx-322 
using  the  same  circuit  as  was  used  in  the  all- 
wave  receiver.  The  plate  voltage  was  135  volts 
and  the  screen  voltage  45  volts,  both  obtained 
from  B  batteries.  Filament  voltage  is  obtained 
by  connecting  the  1.5-  and  2.5-voIt  windings  on 
the  filament  transformer  in  series  as  indicated  in 
the  circuit,  Fig.  2,  so  that  the  voltages  add. 
The  voltage  is  then  reduced  to  3.3  by  means  of 
a  5-ohm  resistance  connected  in  series  with  one 
side  of  the  filament  circuit.  If  the  two  windings 
are  connected  so  that  the  voltages  buck  each 
other  the  filament  of  the  screen-grid  tube  will 
not  light  and  the  connections  to  one  of  the  wind- 


FIG.    2 

ings  should  then  be  reversed.  A  i5OO-ohm  re- 
sistor, by-passed  with  a  o.oi-mfd.  (or  larger) 
fixed  condenser,  is  connected  between  the  center- 
tapped  resistance  and  minus  B  to  supply  C  volt- 
age for  the  grid  of  the  322  type  tube.  The  com- 
plete circuit  is  given  in  Fig.  2. 

This  complete  a.c.  circuit  for  some  reason, 
not  yet  determined,  seems  much  more  tricky 
than  the  d.c.  circuit  of  Fig.  i,  and  in  general, 
the  performance  of  the  circuit  with  a.c.  on  the 
322  filament  was  not  altogether  satisfactory. 
The  operation  of  this  complete  a.c.  model  had 
the  disadvantage  that  the  output  of  the  receiver 
contained  a  loud  hum  when  the  detector  was 
put  into  oscillation  and  the  two  tuning  circuits 
brought  into  resonance.  Apparently  under  such 
conditions  the  322  began  to  oscillate.  A  definite 
increase  occurred  in  the  current  flowing  in  the 
screen  grid  circuit.  This  trouble  was  not  caused 
by  common  coupling  in  the  battery  supplying 
the  screen  circuit  for  the  same  effect  was  no- 
ticed with  a  separate  battery  supply  to  the  screen 
grid. 

When  the  detector  circuit  was  not  oscillating 
the  output  of  the  receiver  was  quiet.  Therefore, 
the  only  practical  disadvantage  of  the  arrange- 
ment was  that  it  made  it  difficult  to  tune-in 
signals,  especially  weak  ones,  by  means  of  a 
squeal  for  the  hum  is  loud  enough  to  make 
a  faint  heterodyne  whistle  inaudible. 

Some  experiments  were  now  made  using  a 
neutralized  circuit.  In  this  model  of  the  "Lab" 
receiver,  the  lead  from  the  plate  of  the  r.f.  am- 
plifier to  the  detector  coil  is  several  inches  long 
and,  although  when  using  a  227  in  a  Rice- 
neutralized  amplifier  the  long  lead  will  have  no 
effect  on  the  stability  of  the  circuit,  it  was 
thought  that  it  might  be  causing  some  trouble 
when  using  a  322  without  neutralization.  We 
therefore  changed  the  circuit  of  the  r.f.  stage  to 
that  given  in  Fig.  3.  The  small  twisted  lead  con- 

Q.6 


nected  to  the  grid  and  plate  of  the  322,  consisted 
of  two  2-inch  lengths  of  insulated  wire  twisted 
together.  These  wires  constituted  a  small  con- 
denser and  were  used  to  increase  the  grid-plate 
capacity  of  the  tube  to  about  o.ooooi  mfd. 
(10  mmfd.)  so  that  the  circuit  might  be  neutral- 
ized with  a  standard  neutralizing  condenser. 
The  neutralized  receiver  gave  somewhat  more 
stable  operation  than  the  unneutralized  circuit 
but  the  hum,  with  the  detector  oscillating,  was 
still  present. 

As  a  result  of  these  experiments  we  are  un- 
able, for  the  present,  to  recommend  the  use  of 
a  322  in  the  "Lab"  circuit  with  its  filament  oper- 
ated on  a.c.  Those  of  our  readers  who  have  a 
d.c.  operated  "Lab"  receiver  may  use  a  322  in 
accordance  with  the  circuit  given  in  Fig.  i 
and  the  receiver  will  give  somewhat  greater 
gain  than  was  obtained  using  a  2Oi-type  tube. 

In  some  cases  it  may  be  found  that  the  selec- 
tivity of  the  circuit  using  a  screen-grid  tube  is 
not  as  good  as  when  using  a  2OI-A  type  tube  as 
the  r.f.  amplifier.  The  selectivity  may  be  im- 
proved, however,  by  substituting  a  midget  vari- 
able condenser  with  a  maximum  capacity  of 
o.oooi  mfd.  for  the  fixed  o.oooi-mfd.  condenser 
connected  between  the  plate  of  the  screen-grid 
tube  and  the  grid  end  of  the  detector  coil.  The 
selectivity  of  the  circuit  may  be  adjusted  to  a 
satisfactory  value  by  varying  the  setting  of  this 
small  condenser. 

The  results  of  these  experiments  will  be  ap- 
plicable to  other  receivers  of  the  same  type  as 
the  "Lab"  set.  To  revise  these  other  receivers 
for  screen-grid  operation,  it  is  simply  necessary 
to  remove  the  connection  to  the  NP  winding, 
i.e.,  the  primary  and  neutralizing  windings  of  the 
r.f.  transformer  and  then  connect  a  lead  from 
the  plate  of  the  322  through  a  condenser  with  a 
capacity  of  about  o.oooi  mfd.  or  larger  to  the 
grid  end  of  the  secondary  coil  in  the  detector's 
grid  circuit.  Voltage  for  the  plate  of  the  screen 
grid  tube  should  be  supplied  through  an  r.f. 
choke,  Fig.  i,  which  should  have  an  inductance 
of  85  millihenries  or  more. 

Experiments,  as  have  been  described  here,  can 
readily  be  duplicated  in  a  home  laboratory. 
To  many  of  our  readers,  experimenting  with 
sets  and  circuits  in  their  own  small  iab.,  equipped 
in  many  cases  with  instruments  made  from  de- 
scriptions that  have  been  given  in  RADIO 
BROADCAST,  is  proving  an  intensely  interesting 
part  of  their  radio  training.  How  much  one  really 
knows  quantitatively  about  radio  engineering, 
depends  almost  directly  upon  how  many  and 
how  systematically  experiments  have  been 
made;  experiments  not  carried  out  with  a  definite 
aim  in  view,  generally  yield  no  concrete  results 
and  do  not  greatly  increase  one's  knowledge  of 
radio  phenomena.  The  Laboratory  will  always 
be  glad  to  hear  from  any  readers  who  do,  or 
have  done,  any  such  experimenting. 


AA[  EAST  SET  TO  BUILD 

Little  explaining  need  be  done  if  this  illustration  is  compared  with  Figs.  I  and  2.  The  "loop  tap"  indicated  by 

the  f  end!  is  not  used  in  this  set  but  is  shown  merely  to  indicate  how  this  type  of  lap  is  made.  In  this  coil,  the 

tap  employed  is  near  the  detector  and  cannot  be  seen  in  this  photograph. 


THE  receiver  illustrated  above  is  sim- 
ple to  built,  costs  but  little,  delivers 
high-quality  signals,  and  is  reasonably 
selective.  It  provides  an  excellent  receiver  for  the 
beginner  to  try  his  hand  at — after  having  put 
together  this  array  of  apparatus  he  has  the  whole 
world  of  radio  home  construction  at  his  feet. 
There  are  many  people  who  would  like  to  listen 
to  local  broadcasting  without  a  great  expenditure 
of  cash,  either  for  the  radio  set  or  for  its  upkeep. 
This  set  will  provide  good  signals  from  broad- 
casting stations  not  too  far  away  at  small  cost. 
The  receiver  consists  of  a  tuner,  a  crystal  de- 
tector, an  amplifier  and  a  pair  of  head  phones. 
Anyone  with  a  soldering  iron  and  a  pair  of  pliers 
can  assemble  it  in  an  hour.  The  disadvantages  of 
the  receiver  are  few:  it  is  not  selective  enough  to 
distinguish  between  stations  operating  within 
30  kc.  of  each  other;  it  will  not  receive  the 
"coast";  but  for  reception  from  locals  or  power- 
ful stations  up  to  100  miles  away  it  is  excellent. 
Because  of  the  special  electrical  characteristics 
of  the  crystal — in  this  case,  a  piece  of  carborun- 
dum— it  is  possible  to  use  a  high-ratio  audio- 
frequency amplifying  transformer.  The  step-up 
as  between  primary  and  secondary  circuits  in 
this  case  is  6:1.  Any  present-day  transformer  of 
such  high  ratio,  used  with  a  vacuum  tube  detec- 
tor circuit  would  give  comparatively  poor  quality 
— the  low  notes  especially  would  suffer. 

The  coil  can  be  made  at  home,  or  any  com- 
mercial coil  may  be  employed  provided  it  has 
the  proper  number  of  turns  to  cover  the  broad- 
casting band  with  the  condenser  used  and  pro- 
vided it  is  not  too  difficult  to  solder  a  few  taps  on 
it.  The  condenser  may  be  any  assembly  that 
happens  to  be  in  the  builder's  junk  box.  Natu- 
rally, the  better  the  coil  and  the  condenser  the 
better  the  final  result. 

A  good  way  to  wind  the  coil  is  to  place  a 
rat  tail  file,  a  pencil  or  a  piece  of  dowel  rod 
through  the  spool  containing  the  wire  which  is 
to  be  wound  on  the  coil  form  and  to  place  the 


By  KEITH  HENNEY 

Director  of  the  Laboratory 

spool  on  the  floor.  Two  holes  are  drilled  in  the 
ends  of  the  coil  form  and  one  end  of  the  wire  from 
the  spoil  is  looped  through  one  of  these  holes.  A 
weight,  one's  feet  for  example,  is  placed  on  the 
rat  tail  file,  and  the  wire  wound  on  the  form. 
The  purpose  of  the  weight  is  to  keep  the  wire 
taut  so  that  it  goes  on  the  form  tight  enough  that 
it  will  not  fall  apart  under  temperature  or  humid- 
ity changes.  When  the  proper  number  of  turns 
has  been  wound,  the  wire  is  cut  and  the  end 
looped  through  the  second  hole  in  the  coil  form. 
The  diagram,  Fig.  i,  indicates  the  exact  number 
of  turns  recommended  for  this  receiver.  Taps 
should  be  made  at  three  places,  dividing 
the  coil  into  four  equal  parts.  These  can  be 
made  by  twisting  a  loop  of  wire  when  it  is  wound 
on  the  form  or  by  soldering  short  lengths  of  wire 
to  places  where  the  insulation  has  been  scraped 
from  the  wire  after  winding.  The  loop  method  is 
shown  in  the  photograph  above. 

Strongest  signals  will  be  obtained  with  the 
antenna  wire  attached  to  one  end  of  the  coil  and 
the  ground  to  the  other.  At  the  same  time  the 
selectivity  will  be  poorest.  To  improve  the  selec- 
tivity, the  antenna  may  be  tapped  on  to  the  coil 
as  shown  in  the  accompanying  illustiation,  or  an 
additional  winding  of  about  10-20  turns  may  be 
wound  about  the  larger  coil  and  the  antenna  and 
ground  attached  to  it.  The  antenna  should  be 
about  75  feet  long. 

Still  greater  selectivity  may  be  obtained  by 
tapping  the  detector  circuit  to  only  a  part  of 
the  coil.  Note  that  this  was  done  in  this  receiver. 
See  Fig.  I.  This  is  because  the  crystal  is  a  low 
impedance  detector  and  increases  the  effective 
resistance  of  the  tuned  circuit  consisting  of  the 
coil  and  condenser.  When  tapped  across  part 
of  the  coil  this  increase  in  resistance,  and  result- 
ing decrease  in  selectivity,  is  not  so  marked. 
The  arrangement  used  in  the  Laboratory  is 
shown  in  Fig.  2.  In  the  Laboratory,  signals 
freer  from  outside  noise  or  "interference"  were 
secured  by  not  grounding  the  crystal  circuit. 

97 


This  may  not  be  the  case  generally  and  for  this 
reason  the  constructor  should  try  grounding  the 
circuit  as  shown  in  the  dotted  lines. 

With  this  receiver,  tested  in  our  Laboratory, 
and  using  the  tapped  arrangement,  it  is  possible 
to  hear  wjz  30  miles  away  when  WEAF  is  operat- 
ing 8  miles  away  although  with  bad  interference. 
With  a  wave-trap  tuned  to  WEAF,  considerable 
improvement  in  wjz's  signals  is  noted,  wjz  can- 
not be  heard  at  all  if  the  detector  is  connected 
across  the  entire  coil. 

The  parts  actually  used  in  the  set  photo- 
graphed follow,  and  any  similar  apparatus  may 
be  used.  It  is  even  possible  to  hear  signals  with 
a  crystal,  home  assembled,  such  as  galena  or 
silicon — a  very  cheap  detector.  The  home 
constructor  is  advised  against  such  procedure. 
The  Carborundum  unit  is  recommended  because 
it  is  a  compact,  stable,  and  sensitive  unit,  and 
because  it  is  possible  to  use  a  biasing  voltage  on 
it  to  increase  its  sensitivity. 

The  constructor  may  use  a  small  flash-light 
cell  as  the  biasing  battery  or  he  may  use  the 
voltage  obtained  from  dry  cells  used  to  light  the 
filament  of  the  amplifier  tube.  Using  the  extra 
cell  is  simpler,  but  has  the  disadvantage  that  it 
is  an  additional  unit  which  needs  replacement. 
If  the  dry  cells  are  used,  the  dotted  lines  in  the 
diagrams  should  be  followed,  or  as  in  the  insert 
in  Fig.  2,  where  the  voltage  drop  across  the 
rheostat  is  used. 

It  does  not  matter  where  the  various  parts  are 
located  on  the  base  board.  One  arrangement  is 
shown  in  the  photograph.  The  picture  wiring 
diagram,  Fig.  i,  shows  where  the  wires  go. 

The  signals  from  this  receiver  may  be  amplified 
by  any  of  the  power  amplifier  units  now  readily 
obtainable.  If  a  two-stage  amplifier  is  used, 
such  as  is  made  by  Samson,  Amertran,  Silver- 
Marshall  or  others,  the  output  of  the  detector 
may  be  used  and  the  amplifier  tube,  transformer, 
and  accessory  apparatus  shown  in  this  model  may 
be  eliminated.  (Dotted  lines  in  Fig.  2) 


RADIO  BROADCAST 


JUNE,  1928! 


The  rheostat  is  used  to  turn  on  and  off  and 
to  control  the  current  through  the  amplifier  fila- 
ment. It  should  never  be  turned  on  further  than 
is  necessary  to  bring  in  the  signals  at  proper 
volume.  An  experiment  will  show  that  turning  it 
beyond  this  point  does  not  increase  signal 
strength.  As  a  matter  of  fact  such  a  procedure 
only  decreases  the  life  of  the  batteries  and  the 
tube.  One  45-volt  B-battery  block  and  three  dry 
cells  will  last  several  months  with  such  a  simple 
receiver. 

After  constructing  such  a  receiver  there  is  the 
possibility  of  adding  another  stage  of  audio 
amplification  for  loud  speaker  signals,  and  the 
Laboratory  will  be  pleased  to  supply  information 
on  how  to  do  this  to  those  who  write.  There  is 
also  the  possibility  of  adding  a  stage  of  radio- 
frequency  amplification  to  such  a  receiver, 


FIG. 
How  to  place  and  connect  the  parts  employed 


Omit  if  used  with  Power 
Amplifier  having_twp_  stages  "_^ 


v-To  one  dry  cell 
FIG.  2 

Circuit  diagram  of  the  crystal  set  and  one  stage  of  audio  amplification.  The  insert 
shows  how  the  detector  bias  may  be  obtained  from  the  voltage  drop  in  the  rheostat 


SIMPLICITY    ITSELF 

The  panel  is  7"  X  12"  and  can  be  fitted  into  any  cabinet  which  suits  the  owner.  The 
Remler  dial  noted  in  the  parts  list  was  not  available  when  this  photograph  was  taken 


thereby  making  it  much  more  selective  and  sensi- 
tive and  as  a  result  to  increase  its  distance- 
getting  ability.  In  fact,  a  three-tube  set  using 
the  Carborundum  unit  as  a  detector  provides 
the  listener  with  a  high  quality,  reasonably  selec- 
tive receiver  for  reception  from  stations  within 
•  several  hundred  miles.  The  Laboratory  has  re- 
ceived a  number  of  letters  from  readers  who  have 
done  very  creditable  DX  work  on  such  an  outfit. 
How  such  a  receiver  as  is  described  here  is 
used  in  RADIO  BROADCAST  Laboratory  may  be  of 
interest.  At  times  considerable  noise  is  picked 
up  in  the  Laboratory  from  the  presses,  which 
print  RADIO  BROADCAST  and  many  other  maga- 
zines, making  the  testing  of  receiving  equipment 
impossible.  Down  at  the  shack,  a  distance  of 
about  looo  feet  from  the  Laboratory  where  2  or 
is  located  the  "air"  is  quiet.  The  receiver  illus- 
trated here  is  installed  there  and  permanently 
tuned  to  WEAF.  The  output  from  the  detector  is 
sufficiently  high  that  it  can  be  placed  on  a  wire 
line  coming  to  the  Laboratory  where  it  is  fed 
into  a  two-stage  amplifier  and  thence  to  a  loud 
speaker.  When  necessary,  the  first-stage  amplifier 
on  the  base  board  with  the  detector  is  thrown 
into  the  circuit  by  means  of  an  extra  line  and 
the  output  from  it  is  put  on  a  third  pair  of  wires. 
This  output  may  be  used  in  connection  with  a 
single  power  stage  or  loud  speaker  operation.  At 
all  times,  when  near-by  broadcasting  stations 
are  on  the  air  we  have  good  signals  available  in 
the  Laboratory  for  testing  purposes. 

THE    LIST   OF    PARTS 

The  experimenter  who  already  has  odds  and 
ends  of  radio  apparatus  in  his  possession  can 
probably  assemble  the  receiver  described  here 
without  the  purchase  of  much  additional  appara- 
tus. The  parts  listed  below  were  used  in  the  re- 
ceiver described,  although  of  course  any  others, 
electrically  and  mechanically  similar  may  be 
selected. 

Ci — Remler  0.0005  mW-  type  No.  639  conden- 
ser Remler  standard  dial 

L2 — 52  turns  No.  24  s.c.c.  copper  wire 

wound  on  3"  form 
LI — 10-20  turns  No.  28  a.s.c.  copper 

wire 
Ti — General    Radio   No.   285    audio 

transformer 
Ri — Frost  3o-ohm  rheostat 

Carborundum    Company    detector 
unit 

Frost  UX  type  socket 

Fahenstock  spring  clips  (8) 
One — ux-igg  vacuum  tube 
One — Westinghouse  Micarta  panel 
One — Wood  baseboard 
3— dry  cells 
One — set  Trimm  headphones 


Phones  or 

Power 
Amplifier 


I  Three  dry 
cells 


T1 


LOUD 

SPEAKER 

JACK 

POWER  TUBE 
SOCKET 


OUTPUT 
TRANSFORMER 
T4 


POWER  LEAD 
fo  110  VOLTS 
60  CYCLE  A.C. 


110  VOLT 
LINE  SWITCH 


FILAMENT 
TRANSFORMED.  T3 


THE  EVER-POPULAR  ROBERTS  SET  WITH  A.  C.  OPERATION 

The  illustration  is  lettered  to  agree  with  the  list  of  [tarts  on  page  101  and  with  Fig.  3.  The  circuit  diagram.  This 
model  of  the  a.c.  Roberts  reflex  circuit  was  built  to  fit  in  a  phonograph  cabinet.   It  is  unnecessary  for  the  con- 
structor to  follow  this  layout  for  wide  latitude  is  allowed  by  this  circuit  in  this  respect 


A  Three-Tube  A*  C, 


By  ELMER  G.  HERY 


F  THE  thousands  of  set-builders  who 
have  constructed  the  original  three-tube 
Roberts,  few  have  been  won  over  to 
any  other  circuit  unless  they  have  gone  to  a 
much  more  elaborate  and  expensive  layout.  For 
those  who  know  the  merits  of  the  Roberts  cir- 
cuit, a.c.  operation  as  described  in  this  article 
is  almost  inevitable. 

Beginners  will  find  in  this  receiver  a  set  which 
is  easy  to  construct  and  uniformly  excellent  in 
results  as  to  the  quality,  selectivity,  sensitivity, 
volume,  and  distance  reception. 

An  important  feature  is  that  this  circuit  does 
not  require  the  most  expensive  pieces  of  equip- 
ment. It  may  be  constructed  from  whatever  ma- 
terials are  at  hand.  The  skeptical  may  make  a 
rough  assembly  of  old  parts,  and  then  convince 
himself  that  the  substitution  of  any  good  low- 
loss  parts  will  give  better  results.  [The  list  of 
parts  and  the  photographs  show  exactly  what 
was  used  in  the  set  described  by  the  writer.  The 
parts  are  all  standard  and  readily  available. 
Wide  substitution  can  be  made,  according  to  the 
desire  of  the  constructor. — Editor.] 

Another  good  feature  is  the  fact  that  the  ar- 
rangement of  parts  and  the  panel  shape  do  not 
affect  the  results.  This  circuit  has  been  built  by 
the  writer  on  square  panels  and  on  long  narrow 
panels,  and  to  fit  in  all  kinds  of  cabinets  with 
excellent  reception  in  all  cases. 

The  first  thing  to  consider  is  the  coils.  Manu- 
factured coils  may  be  used  if  desired.  The  writer 
has  used  Sickles  and  Hammarlund-Roberts  with 
perfect  satisfaction.  If  the  set-builder  desires  to 
make  up  his  own  coils  they  can  easily  be  made. 


Thirteen-point  spider-web  fiber  forms  are  re- 
quired. They  may  be  obtained  from  the  lo-cent 
stores.  The  antenna  coil  consists  of  thirty-five 
turns  wound  over-two-and-under-two  spokes, 
with  a  twisted  loop  or  tap  every  five  turns. 
There  are  two  secondary  coils  Li  and  Lt,  and  each 
consisting  of  forty-four  turns  wound  over-two- 
and-under-two  spokes.  The  tickler  coil,  LS  con- 
sists of  twelve  turns  wound  over-two-and-under- 
two  spokes.  These  four  coils  are  all  made  of  No. 


The  A.  C.  Roberts  Receiver 

THE  Roberts  receiver,  first  introduced  by 
RADIO  BROADCAST  in  1924  won  many  friends 
for  radio  and  many  for  ibis  magazine.  It  has  been 
constructed  by  more  than  100,000  radio  fans  and, 
in  one  form  or  another,  is  still  giving  satisfactory 
service  all  over  the  world.  The  circuit  is  so  effi- 
cient— considering  the  number  of  tubes  employed 
— and  so  easy  to  build  and  operate  that  its  popu- 
larity, like  a  certain  famous  cigarette,  is  deserved. 
Many  readers  are  still  interested  in  building  the 
circuit  and  Mr.  Hery's  article  here  gives  them  full 
instructions  and  a  wide  latitude  in  construction. 
For  those  who  are  interested  in  making  over  their 
present  Roberts  set  for  a.c.  operation,  the  last  part 
of  this  article  provides  sufficient  information.  The 
circuit  shown  here  employs  the  original  reflex  ar- 
rangement. Those  who  desire  to  employ  a  straight 
audio  stage  and  eliminate  the  reflex  may  secure 
information  by  writing  to  our  Technical  Informa- 
tion Service. 

— THE  EDITOR. 


99 


22  double  cotton  covered  wire.  The  NP  coil  Li, 
is  made  of  No.  26  double  cotton  covered  wire. 
This  coil  consists  of  a  double  winding;  that  is, 
two  parallel  wires  wound  over-one-and-under- 
one  spoke,  with  eighteen  turns.  In  other  words, 
there  are  two  concentric  coils  of  eighteen  turns 
each.  The  wire  may  be  twisted  or  kept  flat, 
preferably  the  latter. 

The  antenna  coil  and  its  secondary  coil  are 
mounted  on  the  same  shaft  about  j"  apart.  A 
long  brass  machine  screw  ($\"  or  more)  makes 
an  ideal  mounting  arrangement,  using  a  nut  on 
either  side  of  each  coil  to  hold  it  rigid.  The  ma- 
chine screw  is  bent  to  give  any  desired  mount- 
ing angle  to  the  coils,  and  fastened  through 
the  baseboard  with  a  nut.  (See  Fig.  i)  Fig.  i-B 
also  provides  a  very  simple  mounting  through 
one  of  the  spokes  of  one  coil. 

A  standard  mounting  for  the  tickler  coil  is 
an  arm  with  knob  for  panel  mounting.  The  NP 
and  secondary  coils  may  then  be  mounted  on  a 
screw  through  the  baseboard  as  shown  in  Fig.  2. 
The  dotted  lines  show  the  tickler  coil  in  the 
raised  position. 

It  is  important  that  the  antenna  coil  and  its 
secondary  be  mounted  so  that  the  direction  of 
rotation  of  the  windings  is  the  same  for  both 
coils.  Likewise  the  NP,  Secondary,  and  Tickler 
coils  should  be  wound  in  the  same  direction. 
One  way  to  avoid  trouble  from  this  source 
is  to  proceed  as  follows:  when  the  coils  are 
wound,  mark  on  the  forms  an  arrow  which  points 
around  the  form  in  a  clockwise  direction.  Then, 
starting  from  the  inside  and  proceeding  to  the 
outside  of  the  form,  the  wire  should  be  wound 


100 


RADIO  BROADCAST 


JUNE,  1928 


FIG.     IA-B 
Details  for  mounting  and  tapping  the  coils 

on  in  a  clockwise  direction.  The  coils  in  each 
assembly  should  be  arranged  so  that  all  of  the 
arrow  marked  sides  face  in  the  same  direction. 
The  two  groups  of  coils  should  be  mounted  as 
far  apart  as  mechanically  possible,  and  at  right 
angles  to  each  other. 

After  the  coils  have  been  mounted  and  the 
positions  of  the  other  pieces  of  equipment  have 
been  determined,  the  inside  and  outside  leads  of 
each  coil  may  be  brought  to  the  most  convenient 
spoke  of  the  spider-web  form,  and  fastened 
through  a  hole  in  the  spoke  by  means  of  a  screw 
and  nut  (see  diagrams).  Then  the  spokes  may 
be  cut  off  to  within  f"  of  the  wire  on  the  coil, 
thus  reducing  the  over-all  size  of  the  coils. 
For  connections,  the  outside  and  inside  leads 
of  coils  are  indicated  on  the  wiring  diagram  by 
"O"  and  "I"  respectively.  The  center  point  of 
the  NP  is  coil  indicated  by  "M."  The  coils  as 
they  appear  on  the  wiring  diagram,  Fig  3,  from 
left  to  right  are  as  follows:  Antenna,  LI,  antenna 
secondary,  Lj,  NP,  La,  and  Ln,  secondary,  L4,  and 
above  the  secondary,  the  tickler  coil,  Lj. 

The  taps  on  the  antenna  coil  may  be  connected 
to  an  inductance  switch  if  desired,  but  a  simpler 
method  is  to  place  a  test  clip  (See  Fig.  I  A)  on  the 
end  of  the  ground  lead,  and  clip  to  the  tap  which 
gives  the  best  results.  The  longer  the  antenna 
in  use,  the  fewer  turns  will  be  required  on  the 
antenna  coil.  One  tap  will  be  found  which  will 
give  satisfactory  results  on  all  wavelengths. 

The  method  of  obtaining  the  mid-point  "M" 
of  the  NP  coil  may  require  some  explanation. 
"M"  is  obtained  by  connecting  the  inside  end 
of  one  winding  with  the  outside  end  of  the  other 
winding.  Two  different  colors  of  wire  may  be 
used  to  avoid  confusing  the  two  windings,  or  a 
flashlight  bulb  may  be  lighted  through  each 


winding  to  locate  the  corresponding  inside  and 
outside  ends. 

LOCATING   THE    APPARATUS 

THERE  is  nothing  special  to  be  said  about  the 
locating  or  mounting  of  the  remaining  equip- 
ment, with  the  exception,  of  course,  that  the  grid 
and  plate  leads  should  be  kept  short.  The  photo- 
graphs give  an  idea  of  a  good  baseboard  layout 
which  was  designed  to  fit  a  phonograph  cabinet 
and  to  include  all  the  a.c.  power  supply  appara- 
tus. The  panel  layout  suggested  may  easily  be 
modified  to  suit  the  size  and  shape  of  the  panel 
used  by  the  constructor  who  duplicates  this  re- 
ceiver. 

The  switch  mounted  on  the  panel  controls 
the  line  current  supply  and  should  be  of  a  size 
and  capacity  equal  to  wall  switches  used  for 
house  lighting.  A  simple  method  is  to  use  the 
body  of  any  ordinary  no-volt  tumbler  switch 
and  mount  it  directly  on  the  panel  with  a  slot 
cut  in  the  panel  for  the  lever. 

No  rheostats  are  needed  when  the  a.c.  tubes 
are  used,  and  the  volume  control  may  be  a 
25,ooo-ohm  potentiometer  in  the  antenna  circuit 
or  the  volume  control  may  be  as  indicated  in  the 
model  described  here,  i.e.,  a  variable  resistance 
such  as  a  Clarostat  or  Bradleyohm  across  the 
secondary  of  the  first  audio  transformer.  No 
loud  speaker  jack  is  shown  on  the  panel,  as 
modern  practice  tends  toward  mounting  this 
at  the  back  of  the  set  if  it  is  used  at  all,  with 
the  antenna  and  ground  binding  posts. 

As  to  the  make  of  tubes  to  be  used,  there  is 
little  choice  between  standard,  reliable  prod- 
ucts. There  has  been  considerable  doubt  on  the 
part  of  prospective  set-builders  as  to  whether  the 
a.c.  tubes  will  give  very  long  usage.  For  those 
who  prefer  to  make  certain,  a  written  guarantee 
is  given  with  some  makes  to  replace  tubes  free 
of  charge  if  they  fail  to  function  for  one  year. 
This  should  satisfy  the  demands  of  the  most  ex- 
acting buyer.  This  article  describes  the  use  of 
a.c.  tubes  which  employ  the  Radiotron  type 
bases,  although  the  set  will  work  excellently 
with  the  Sovereign  or  Kellogg  a.c.  tubes.  In  the 
event  that  the  builder  uses  this  type  of  tube, 
the  major  difference  between  that  construction 
and  this  is  in  the  a.c.  filament  circuit. 

No  rules  need  be  observed  in  the  assembling 
of  the  set,  except  that  the  filament  leads  should 
be  isolated  as  far  as  possible  from  all  other 
leads,  and  especially  from  grid  leads.  The  pho- 


FIG.    3 

Diagram  of  connections.  Those  who  desire  to  convert  their  d.  c.  Roberts  sets 
can  follow  this  diagram  and  instructions  on  this  page  and  the  one  following 


'•.-  Base    Board 

FIG.    2 
The  coils  and  their  relation  to  the  panel 

tographs  show  how  this  may  be  accomplished. 
It  is  undoubtedly  wise  to  complete  all  other 
wiring  of  the  set  before  starting  the  filament 
wiring,  to  avoid  any  possibility  of  connecting 
filament  leads  to  any  other  part  of  the  circuit. 

The  filament  current  may  be  obtained  from 
a  filament  transformer.  If  a  1 12  or  171  type  tube 
is  to  be  used  for  the  last  amplifier,  the  filament 
transformer  should  have  three  voltages;  namely, 
i^  volts,  2j  volts,  and  5  volts.  Some  B  power 
units  provide  a  5-volt  winding  which  may  be 
used  for  the  amplifier  tube,  in  which  case  only 
the  two  lower  voltages  need  be  supplied  by  the 
filament  transformer.  If  a  210  type  tube  is  used 
for  an  amplifier  yj  volts  are  required  for  the 
filament,  and  this  voltage  is  usually  provided  in 
the  power  pack  or  powerizer  being  used  for  plate 
current. 

Any  good  filament  transformer  may  be  used, 
some  makes  furnishing  mid-taps  for  the  2|-volt 
and  5-volt  windings.  It  is  not  wise  to  use  a  mid- 
tap  in  the  transformer  on  so  low  a  voltage  as 
I  j,  so  that  instead  a  mid-tap  resistance  or  a  po- 
tentiometer, Re,  is  used  to  obtain  the  mid-point 
of  the  ij-volt  winding.  The  mid  points  of  the 
2j-volt  and  5-volt  windings  may  be  obtained 
in  the  same  manner  if  the  transformer  is  not 
provided  with  mid-taps. 

SECURING   GRID    BIAS 

FOR  grid  bias  on  the  reflexed  tube,  the  center 
point  of  the  mid-tap  resistance  is  connected 
to  one  side  of  a  looo-ohm  resistor,  Ri,  The  other 
side  of  the  resistor  is  connected  to  ground  and 
there  is  a  i.o-mfd.  condenser,  C;,  across  the  re- 
sistor. For  grid  bias  of  the  power  tube,  the  mid- 
tap  of  the  filament  transformer  winding  supply- 
ing this  tube  is  connected  to  a  resistance  of 
2000  ohms,  Rs,  the  other  side  of  which  is  con- 
nected to  ground.  A  i.o-mfd.  condenser  Cs  is 
placed  across  this  resistance.  This  value  of  re- 
sistance is  satisfactory  for  112  and  171  type 
tubes. 

Some  tube  manufacturers  recommend  a  posi- 
tive grid  bias  for  the  heater  of  the  detector  tube, 
and  some  recommend  negative  bias.  In  this  cir- 
cuit no  bias  has  been  found  necessary.  The  mid- 
tap  lead  of  the  2^-volt  winding  may  be  con- 
nected to  plus  45  instead  of  to  ground  in  the  event 
that  there  is  excessive  hum  in  the  output  of  the 
receiver. 

A  227  type  tube  may  be  used  in  the  reflex 
position  if  desired,  but  satisfactory  results  should 
be  obtained  with  the  226  type,  and  this  type 
is  somewhat  cheaper  than  the  227  type. 

Each  pair  of  filament  leads  must  be  twisted 
with  about  two  or  three  twists  to  the  inch  to 
avoid  hum.  Likewise,  the  leads  which  go  to  the 
tumbler  switch  on  the  panel  should  be  twisted, 
as  well  as  any  other  a.c.  leads  in  or  around  the 
set.  For  filament  wiring,  no  smaller  wire  than 
No.  14  should  be  used,  as  the  a.c.  tubes  draw  a 
much  heavier  current  than  the  d.c.  tubes.  For 


JUNE,  1928 


A  THREE-TUBE  A.  C.  OPERATED  ROBERTS  RECEIVER 


101 


wiring  the  balance  of  the  set  Celatsite 
or  similar  hook-up  wire  is  recom- 
mended. 

CONVERTING    YOUR    D.    C.    ROBERTS 

FOR  the  conversion  of  a  storage- 
battery-operated  Roberts  set  to 
complete  a.c.  operation,  the  'wiring 
diagram  and  the  instructions  already 
given  are  perhaps  sufficient.  The  sub- 
stitution of  a  B-  power  unit  for  a  B 
battery  needs  no  explanation.  Ob- 
taining grid  bias  without  C  bat- 
teries, though  sometimes  confusing, 
should  be  clear  from  the  diagram. 
A  C-battery  in  the  grid  circuit 
puts  the  grid  voltage  below  the  filament 
voltage,  whereas  a  resistance  between  the 
filament  circuit  and  ground  places  the  filament 
voltage  above  the  grid  voltage.  The  effect 
is  the  same  in  either  case.  The  C  batteries 
may  first  be  removed  and  connections  made  in 
their  place  as  shown  in  the  diagram.  Next,  the 
filament  leads  of  each  tube  in  the  d.c.-operated 
set  may  be  increased  in  size  if  necessary  to  carry 
the  heavier  current  taken  by  a.c.  tubes.  [Wire 
tables  showing  current  carrying  capacity  will 
give  this  information.  Or  see  RADIO  BROADCAST 
Laboratory  Information  Sheet  No.  141,  Nov- 
ember, 1927,  issue. — Editor.)  Care  must  be  taken 
in  this  changeover  to  a.c.  not  to  remove  any  leads 
which  serve  some  purpose  other  than  lighting  the 
d.c.  filaments.  A  "UY"  socket  may  now  be  sub- 
stituted for  the  ux  socket  in  the  detector  posi- 
tion, and  the  same  grid  and  plate  leads  that 
were  connected  to  the  ux  socket  go  to  the  UY 
socket.  If  an  output  transformer  or  filter  is  not 
in  use,  one  should  be  installed  as  shown. 

In  the  list  of  parts  given  here,  some  names  of 
equipment  are  mentioned  because  of  successful 
experience  with  these  makes.  Perhaps  other 
makes  will  give  equally  good  or  even  better 
results,  but  some  experimenters  often  like  to  have 
something  definite  in  mind  when  they  do  their 
purchasing.  In  the  case  of  the  variable  conden- 


THE  ALL  IMPORTANT  CONTROLS  ARE  HERE 

sers,  a  rugged  low-loss  construction  such  as 
General  Radio  is  strongly  recommended.  The 
parts  required  for  conversion  of  the  d.c.  set  to 
a.c.  are  indicated  separately  at  the  end  of  the  list. 
The  values  given  for  fixed  condensers,  resis- 
tances, etc.,  will  generally  be  found  satisfactory, 
but  they  may  be  experimented  with  after  the 
set  is  in  operation,  for  possible  improvement 
to  suit  the  taste  of  the  user. 

LIST   OF    PARTS    USED 

Ci,  Cj — General  Radio  o.ooo5-mfd.  variable 
condensers. 

C3 — Hammarlund  g-plate  neutralizing  con- 
denser. 

Ct — Dubilier  o.ooo25-mfd.  fixed  condenser 
with  clips. 

Q — Dubilier  o.oooj-mfd.  bypass  condensers. 

Ce — Dubilier  o.oo25-mfd.  bypass  condenser. 

C?,  Cs — Aerovox  i.o-mfd.  bypass  conden- 
sers. 

RI — Clarostat  volume  control  resistor. 

R2 — Tobe  Tipon  grid  leak  (about  2.o-meg.  al- 
although  various  values  should  be  tried). 

Rs — Hardwick-Field  C-bias  resistor,  2900- 
ohms. 

Ri — Ward-Leonard  C-bias  resistor,  1000 
ohms. 

Ri, — General  Radio  center-tapped  resistor. 

Ti — Amertran  AF-6,  5:1  audio  transformer. 


T2 — Thordarson  R-2OO  audio  trans- 
former. 

T» — Acme  Apparatus  AC-2  filament 
transformer. 

T4 — Bremer-Tully  output  device. 

—Frost  open-circuit  jack. 

— General  Electric  tumbler  switch. 

5 — Spiderweb  coil  forms  and  2  coil 
mounting  arms. 

— Wire  for  coils:  j-lb.  No.  22  d.c. c.; 
J-lb.  No.  26  d.c.c. 

2 — Benjamin  ux  sockets. 

I — Benjamin   UY   socket. 

2 — Marco  dials. 

5 — Eby  binding  posts. 

— No.  14  lamp  cord  for  a.c.   circuit. 

— 25  ft.  Celatsite  hook-up  wire. 

Test  clips,  screws,  nuts,  baseboard, 
and  Westinghouse  Micarta  panel. 

ADDITIONAL    PARTS 

i  —  B-power    unit    supplying    the    following 

voltages:  45,  90,  135,  180 
i — Type  227  a.c.  tube 
I — Type  226  a.c.  tube, 
i — Semi-power  tube,  either  112  or  171  type 

The  coils  used  in  the  set  described  are 
home-constructed  according  to  directions 
in  the  article.  Sickles  or  Hammarlund- 
Roberts  coils  may  be  used  if  the  builder 
prefers  to  use  manufactured  coils. 

The  circuit  and  building  instructions  deal 
with  the  226  and  227  type  of  a.c.  tube 
although  as  indicated  in  the  article,  the 
Sovereign  or  Kellogg  heater  type  a.c.  tubes 
can  be  employed  equally  well  if  the  con- 
structor makes  the  necessary  filament 
circuit  and  mechanical  changes  required. 

If  one  has  on  hand  a  d.c.-operated  Roberts 
receiver  which  is  to  be  changed  over  to  a.c.  . 
operation,  it  will  of  course  be  possible  to  use  in 
the  revised  set  most  of  the  parts  contained  in 
the  d.c.  model.  Only  the  following  items  in  the 
above  list  of  parts  need  be  purchased,  in  chang- 
ing a  set  from  d.c.  to  a.c.  operation:  Cy,  C«,  Rs,  RI 
Re,  T3,  one  Y  type  socket  and  a  line  switch. 


THE    BASEBOARD    ALLOWS    ROOM    FOR    A    B-POWER    UNIT 
This  provides  complete  a.c.  operation  with  maximum  simplicity 


hhX  II 


KY 


The  Simplest  Receiver 


N  A  recent  visit  to  KDKA  I  had  demon- 
strated to  me  the  simplest  and  most  in- 
expensive radio  receiver  in  the  world. 
Although  generally  cautious  in  the  use  of  super- 
latives, in  this  case  I  use  them  without  fear  of 
contradiction.  The  cost  of  the  receiver  in  ques- 
tion is  precisely  nothing.  It  is  exceedingly 
compact;  you  could  hide  it  under  either  half  of 
your  mustache,  although  it  might  not  be  con- 
venient to  keep  it  there.  It  is  portable;  you  can 
carry  it  around  the  house,  or  outside,  set  it  up 
in  an  instant,  and  when  you  don't  want  it,  it 
disappears.  It  provides  a  loud  speaker  signal  of 
moderate  intensity.  The  loud  speaker  is  con- 
tained in  the  set.  There  are  no  knobs,  tuning  con- 
trols, or  adjustments  of  any  kind;  a  child  can 
operate  this  receiver  just  as  well  as  a  radio 
engineer.  It  requires  no  antenna  and  no  battery 
or  power  supply  of  any  description.  The  main- 
tenance cost,  it  follows,  is  nil.  In  these  respects 
it  is  certainly  the  ideal  broadcast  receiver. 

It  has  only  two  faults,  which,  in  all  honesty, 
I  shall  now  reveal.  It  will  not  receive  any  other 
station  than  KDKA.  The  tone  is  decidedly  thin. 

The  technical  gentlemen  of  the  Westinghouse 
Company  can  produce  any  reasonable  number  of 
these  radio  receivers  on  the  transmitter  grounds 
on  a  moment's  notice.  All  they  do  is  to  pick  up  a 
nail  or  piece  of  metal  and  touch  it  to  a  spike  in 
one  of  the  wooden  poles  which  support  the 
antenna.  Withdrawing  the  bit  of  metal  slightly, 
the  experimenter  pulls  out  an  arc  a  quarter  or 
half  inch  long.  He  is  thus  drawing  out  of  the  air, 
according  to  orthodox  radio  principles,  a  few 
watts  of  the  fairly  considerable  number  which 
KDKA  is  flinging  prodigally  over  the  Pennsylvania 
hills.  As  this  radio-frequency  arc  is  modulated, 
it  sings  shrilly  in  accordance  with  the  voice  or 
music  which  is  agitating  the  KDKA  carrier  at  the 
moment.  It  is  a  radio  receiving  set,  with  all  the 
virtues  that  I  have  claimed  for  it.  And  when  you 
are  through  with  it  you  toss  the  nail  away. 

This  receiver  possesses  one  other  convenience 
which,  as  far  as  I  know,  is  incorporated  in  no 
other  instrument  of  its  class,  and  is  found  lack- 
ing even  in  $3000  outfits  built  for  barons  and 
millionaires.  You  can  light  a  cigarette  with  it! 

Operation  of  Broadcasting  Stations 

2O.  FIELD  STRENGTH  MEASUREMENTS 

MOST  operators  of  broadcast  transmitters 
have  only  the  vaguest  sort  of  idea  of 
what  their  outfits  are  actually  doing,  in 
the  way  of  providing  a  signal  for  listeners,  even 
in  their  immediate  neighborhoods.  A  broadcast- 
ing station  depends  on  its  listeners  just  as  much 
as  a  newspaper  depends  on  its  readers,  or  a  gas 
or  electric  power  company  on  its  customers.  The 
newspaper  comparison  is  closer  from  the  practi- 
cal commercial  angle,  while  physically  the  gas  or 
power  company  analogy  is  quite  exact.  The 
broadcast  transmitter  must  provide  a  certain 
radio-frequency  pressure  for  the  listeners  whom 
it  wants  to  reach,  just  as  the  gas  company  must 
maintain  a  certain  gas  pressure  if  it  wants  to  sell 
gas,  and  the  electric  power  concern  must  keep  a 
fixed  electric  potential  between  its  wires.  The 
difference  is  that  the  power  and  gas  companies 
know  what  that  pressure  is,  whereas  the  broad- 


caster generally  does  not.  Yet  there  is  no  great 
mystery  about  the  matter.  The  field  intensity 
of  a  radio  transmitter  can  be  measured,  not  as 
simply  as  gas  and  electrical  pressures,  but  with 
an  amount  of  cost  and  trouble  which  is  cer- 
tainly not  prohibitive  considering  the  funda- 
mental importance  of  the  knowledge  gained  and 
the  fact  that  a  large  investment  is  often  in- 
volved. Every  broadcast  technician  should  at 
least  know  the  general  theory  of  field  intensity 
measurements  and  calculations. 

The  principal  articles  in  the  I.   R.   E.    Pro- 
ceedings are  the  following: 

Englund,  C.  R. :  "Note  on  the  Measurement  of 
Radio  Signals,"  Vol.  II,  No.  I,  Feb.,  1923. 

Bown,  Ralph;  Englund,  C.  R.;  and  Friis,  H.  T.: 
"Radio  Transmission  Measurements,"  Vol.  n, 
April,  1923. 

Austin,  L.  W.  and  Judson,  E.  B.:  "A  Method  of 
Measuring  Radio  Field  Intensities  and  Atmos- 
pheric Disturbances,"  Vol.  12,  No.  5,  October, 
1924. 

Jensen,  A.  G.:  "Portable  Receiving  Sets  for 
Measuring  Field  Strengths  at  Broadcasting 
Frequencies,"  Vol.  14,  No.  3,  June,  1926. 

Friis,   H.  T.  and    Bruce,   E.:  "A   Radio  Field- 

Vacuum-Tube  Voltmeter 


Is  hr  hs 
Ir  =    120  X    - 


LOOP 

• 

( 

!/. 

— 
1.0  mfcT 

(cT 

m 

} 

-  '16V.-- 

(VWWWW^ 

36 

6V. 

Size  of  loop,    103  cm.  square 
No.  of  turns.  5 

Inductance,   77  microhenries 
Resistance.3.5  ohms 

FIG.    I 


Strength  Measuring  System  for  Frequencies  up 
to  Forty  Megacycles."  Vol.  14,  No.  4,  August, 
1926. 

For  those  who  do  not  wish  to  consult  the 
sources  listed  above  a  brief  outline  of  the  sub- 
ject is  presented  here. 

A  transmitting  antenna,  with  a  certain  amount 
of  radio-frequency  current  flowing  in  it,  sets  up  a 
moving  field  of  electric  force  which  is  expressed 
in  volts  per  meter,  or  in  some  more  convenient 
units,  such  as  millivolts  or  microvolts  per  meter. 
This  simply  means  that  if  a  receiving  antenna  is 
put  up  within  range  it  will  be  charged  by  that 
field  to  a  certain  radio-frequency  potential  for 
each  meter  of  its  electrical  height.  The  field 
strength  of  a  5-kw.  broadcasting  station,  about 
ten  miles  away  across  fairly  good  transmission 
territory,  may  be  of  the  order  of  30  millivolts  per 
meter,  to  give  a  practical  illustration.  Then  if  a 
listener  puts  up  an  outdoor  antenna  with  an 
electrical  height  of  3  meters,  he  will  get  90  milli- 
volts from  that  transmitter  to  put  into  his  re- 
ceiver. The  electrical  height  is  less  than  the 
physical  height  (one-half  is  a  common  ratio). 
It  is  a  measure  of  electro-magnetic  effectiveness 
in  transmission  and  reception.  Its  meaning  may 
be  better  understood  after  a  study  of  the  basic 
absorptionless  transmission  formulas: 

102 


(0 

where  lr  is  the  received  antenna  current  in 
amperes,  Is  the  transmitter  antenna  current  in 
amperes,  X  wavelength  in  meters,  f  the  fre- 
quency in  kilocycles,  h,  the  effective  or  elec- 
trical height  of  the  receiving  antenna,  in  meters, 
hs  the  effective  height  of  the  transmitting  an- 
tenna, in  meters,  d  the  distance  in  meters  be- 
tween the  antennas,  and  R  is  the  resistance  of 
the  receiving  antenna. 

The  transmitting  current  may  be  measured 
by  means  of  a  thermo-ammeter  in  the  base  of 
the  antenna.  The  wavelength  and  frequency 
are  known,  if  only  because  the  Federal  Radio 
Commission  and  the  Department  of  Commerce 
insist  on  quite  accurate  data  on  this  point.  The 
resistance  of  the  receiving  antenna  at  the  partic- 
ular frequency  in  question  may  be  measured 
by  the  added  resistance  method.  (See  Circular 
of  the  Bureau  of  Standards,  No.  74.  "Resistance 
Measurement.")  The  distance  d  is  a  factor  which 
may  be  set  by  placing  a  receiver  a  few  wave- 
lengths from  the  transmitter,  and  then  \,  will 
be  sufficiently  high  so  that  it  may  be  measured  in 
the  receiving  antenna  directly  by  means  of  a 
thermo-galvanometer  or  thermo-milliammeter, 
or  the  voltage  across  a  receiving  loop  may  be 
found  by  means  of  a  vacuum-tube  voltmeter. 
Thus  the  product  of  the  two  effective  antenna 
heights,  hr  hs  may  be  calculated  from  (i),  re- 
written as  follows: 

losd  R  I, 

hr  hs  —    1  (2  ) 

40  1C  Is  f 

Of  course  this  does  not  give  us  either  hr  or  hs 
individually.  As  stated  before,  h,  may  be  ap- 
proximated by  taking  half  the  physical  height 
of  the  flat-top  of  the  receiving  antenna  above 
ground,  if  it  is  well  removed  from  absorbing 
objects.  Or,  in  the  case  of  a  loop  antenna,  it  may 
be  calculated  by  a  formula  which  is  derived  from 
our  knowledge  of  the  mechanism  of  radio  trans- 
mission and  the  nature  of  radio-frequency 
pick-up  by  a  loop  or  coil  antenna,  which  responds 
to  the  electro-magnetic  component  of  the  wave. 
With  the  loop  turned  end-on  to  the  direction  of 
radiation,  and  the  antenna  effect  disregarded, 
the  effective  height  is  given  by: 

Area  X  Number  of  Turns  ,  , 

„,.,*_  __  (}) 

Thus  hr  and  hs  may  both  be  determined. 

The  quantity  hs  is  also  of  importance  in  that 
it  is  a  measure  of  the  radiating  efficiency  of  the 
transmitting  antenna.  This  radiation  resistance, 
as  it  is  called,  is  a  part  of  the  total  resistance  of 
the  antenna.  An  antenna,  like  any  other  energy- 
converting  device,  has  losses.  The  ohmic  or  heat 
loss  incidental  to  currents  flowing  in  a  conductor 
is  one  of  them.  Then  there  are  dielectric  losses 
in  the  ground  or  in  objects  near  the  antenna. 
These  are  actual  losses  of  energy  similar  to  the 
losses  caused  by  windage,  winding  resistance, 
and  mechanical  friction  in  an  electric  motor. 
But  an  antenna  is  peculiar  in  that  it  has  one 
type  of  loss  of  energy  which  it  is  definitely 
designed  for,  which  is  its  reason  for  existence. 
It  radiates  energy,  which  is  purposely  lost  so 
that  it  may  be  picked  up  elsewhere  for  the 
communication  of  intelligence.  The  total  power 
dissipated  in  the  antenna  is  given  by: 


JUNE,  1928 


FIELD  STRENGTH  MEASUREMENTS 


103 


Pt  =  Is«  Rt  (4) 

The  radiated  portion  is  given  by: 

Pr  =  U>  Rr 

Rr  =  1600  !jf  Ohms  (5) 

where  Rt  is  the  total  transmitting  antenna  re- 
sistance, R,  is  the  radiation  resistance,  and  h, 
and  >.  are  in  the  same  units  of  length.  Thus  when 
we  have  determined  the  radiation  resistance  of 
the  transmitting  antenna  by  the  procedure 
which  is  outlined  by  formulas  I  to  5,  we  have 
some  idea  of  the  energy  radiated  by  the  trans- 
mitting antenna,  which  means  that  we  know 
the  fundamental  quantity  in  the  physical  func- 
tioning of  the  station  when  it  is  "on  the  air," 
We  know  how  much  of  the  power  we  put  into  it 
is  getting  away  from  the  station. 

A  practical  little  summary  of  work  in  field 
intensity  determinations  is  the  pamphlet  by 
R.  O.  Cherry,  prepared  under  the  direction  of 
Professor  T.  H.  Laby,  on  "Signal  Strength 
Measurements  oj  3/.0,  Melbourne."  The  measure- 
ing  set  consisted  of  a  loop,  a  tuning  condenser, 
and  a  thermionic  voltmeter  to  measure  the 
potential  induced  in  the  loop  by  the  broadcast- 
ing station.  The  voltmeter  was  an  instrument 
of  the  Moullin  type,  manufactured  by  the 
Cambridge  Instrument  Company,  using  plate 
rectification  to  cover  a  scale  of  0-1.5  volts. 
Cherry's  pamphlet  does  not  show  the  voltmeter 
circuit,  but  this  has  been  reproduced  in  Fig.  I 
of  the  present  description,  from  page  35  of 
Moullin's  "  The  Theory  and  Practice  oj  High- 
Frequency  Measurements"  (Charles  Griffin  & 
Co.,  Ltd.,  London),  an  excellent  work  which 
has  been  reviewed  in  this  magazine.  Moullin's 
Fig.  25,  added  to  Cherry's  Fig.  I,  gives  us  our 
Fig.  i.  In  the  manufactured  form  of  the  instru- 
ment the  plate  battery  is  dispensed  with  and  the 
i.6-volt  negative  grid  bias  is  secured  from  the 
6-volt  battery  used  to  light  the  filament  of  the 
tube.  Aside  from  this  battery  the  voltmeter  is 
self-contained.  The  calibration  is  stated  to  be 
independent  of  frequency  and  the  galvanometer 
reads  directly  in  volts,  1.5  volts  r.  m.  s.  being 
full-scale.  When  the  applied  potential  difference 
exceeds  0.4  volt,  grid  current  flows  at  the  peak 
of  the  positive  half  cycle,  and  the  instrument 
draws  a  slight  amount  of  power,  the  apparent 
resistance  at  full  scale  being  of  the  order  of  0.75 
megohms,  corresponding  to  a  power  absorption 
of  2.5  microwatts.  The  voltmeter  is  used  with 
British  valves  intended  for  a  4-5  volt  filament 
potential,  which  is  reduced  to  3.5  volts  in  this 
case,  thereby  prolonging  the  life  of  the  valve 
and  the  calibration  of  the  voltmeter,  barring 
accidents,  almost  indefinitely. 

The  3LO  report  starts  off  with  Formula  (3) 
of  the  present  discussion,  followed  by  an  expres- 
sion for  the  field  strength,  whose  equivalent  is: 

E  •  h,  v  ,  +  wi  L,  (6) 

K2 

where  E,  in  volts  per  meter,  is  the  field  strength 
at  the  point  of  reception;  V,  in  volts,  is  the 
potential  difference  measured  across  the  loop; 
hr,  in  meters,  is  the  effective  height  of  the  loop 
w  =  2xf,  where  f  is  the  radiated  frequency;  L  is  the 
inductance  of  the  loop  in  henrys;  and  R  is  the 
high-frequency  resistance  of  the  receiving  cir- 
cuit, at  the  frequency  f. 

It  is  easy  to  see  how,  according  to  (6)  the 
field  strength,  by  definition,  will  equal  the  re- 
ceived voltage  divided  by  the  effective  height 
of  the  receiver,  but  the  origin  of  the  square  root 
factor  may  not  be  clear.  Cherry  gives  no  explana- 
tion, so  it  may  be  added  that  the  expression  with- 
out the  added  factor  would  be  true  for  an  open 
loop  picking  up  a  voltage  from  the  transmitting 
station  in  question,  but  in  practice  it  is  necessary 
to  tune  the  loop,  as  shown  in  Fig.  i,  both  in 


order  to  select  the  e.  m.  f.  from  the  desired 
station,  and  in  order  to  get  enough  voltage  to 
measure.  But  then  we  are  measuring  the  resonance 
e.  m.  f.  of  the  loop  circuit,  and  this  must  be  cor- 
rected by  -./!••  w2 


^-  before  we  can  deduce  the 


field  strength. 

The  next  step  is  to  measure  or  calculate  the 
inductance  of  the  loop.  For  the  calculation 
process  the  reader  is  referred  to  the  Bureau  of 
Standards  circular  cited  above.  If  a  calibrated 
local  oscillator  is  available,  and  the  condenser 
across  the  loop  also  has  a  known  calibration, 
the  distributed  capacity  of  the  loop  may  be 
determined,  and  the  inductance  is  then  easily 
calculable  from  the  wavelength  formula: 

X  =  1.885  x  IO'V/TC  (7) 

where  C  is  the  total  capacity  (loop     capacity 
plus  condenser  capacity). 

Fig.  2  shows  a  curve  of  wavelength  against 
various  capacities  of  the  tuning  condenser  when 
the  loop  circuit  is  tuned  to  different  frequency 
settings  of  the  oscillator  coupled  to  it.  The 
line  being  extrapolated,  the  point  where  it  cuts 
the  X-axis  (zero  wavelength)  gives  the  dis- 


DISTRIBUTED  CAPACITY  OF  LOOP 


2000 


°  1000 


/ 

•^ 

^ 

S 

/ 

/ 

S 

^ 

!   0  100  200  300  400  500  600  700  80 
CAPACITY  MMFD. 
FIG.  2 

tributed  capacity  of  the  loop.  In  the  case  of  the 
3  LO  experiment  the  wavelength  was  371  meters, 
and  the  loop  capacity  was  found  to  be  65  micro- 
microfarads,  which,  added  to  the  condenser 
capacity  for  resonance,  gave  a  total  capacity  of 
505  micro-microfarads,  whereupon  substitution 
in  (7)  gives:  _ 

371  =  1.885  X  io'i/Lx  505  x  10  •» 
L  =  7.698  x  lo-5  Henry 
=  77  Microhenrys 

The  resistance  of  the  loop,  condenser,  and 
voltmeter  circuit  must  also  be  measured. 
Cherry  gives  the  procedure,  but  instead  of  re- 
peating it  I  shall  refer  those  who  have  a  practical 
interest  in  the  problem  to  Circular  No.  74  again. 
The  mean  of  several  measurements  in  the 
particular  example  we  are  following  was  3.5 
ohms.  A  source  of  inaccuracy  which  must  be 
considered  at  this  point  is  that  the  resistance  of 
the  thermionic  voltmeter  is  not  quite  constant, 
introducing  a  variable  loss,  which  Cherry  be- 
lieves is  between  0.5  and  0.9  ohm  equivalent 
series  resistance.  This  will  result  in  a  slightly  low 
value  for  the  higher  field  strengths,  but  as  such 
measurements,  made  with  a  loop,  are  not  good 
to  better  than  5-10  per  cent.,  a  mean  value  for 
the  high-frequency  resistance  of  the  receiving 
circuit  is  sufficient  for  practical  purposes. 

All  the  other  quantities  needed  for  the  calcula- 
tion, first  of  the  effective  height  of  the  loop 
(Formula  3),  then  of  the  field  strength  (Formula 
6),  are  known.  Using  Formula  3,  we  may  write: 


371 

both  the  length  of  the  side  of  the  loop,  which, 
squared,  gives  the  area,  and  the  wavelength, 
being  expressed  in  meters;  the  result  gives  h,, 
also  in  meters,  as  0.090.  To  get  E  from  (6)  we 

w  L 

must  find  the  value  of  -fr~;  w  is  2x  f,  and  f  is  the 

frequency  corresponding  to  a  wavelength  of 
371  meters;  this  may  either  be  looked  up  in  a 
wavelength-frequency  table  or  calculated  from 


the  basic  relationship  that  the  frequency  is  the 
velocity  of  light  (3x10*  meters  per  second) 
divided  by  the  wavelength,  whence: 

w  =  2  x  LjLJS?  =  5.08  x  ,0. 

and  =i  =  (5.08)  (.0.)  (77)  do-*)  _ 
R  3.5 

So  finally  we  get    E  -  ; ^ — r  -  — 

(0.09)  (112)       10.1 

This  gives  us  the  field  strength  in  terms  of  the 
reading  of  the  thermionic  voltmeter,  divided  by 
a  substantially  constant  factor,  as  long  as  the 
same  loop,  condenser,  and  voltmeter  are  used, 
and  the  wavelength  remains  the  same.  The  loop, 
of  course,  is  turned  to  secure  a  maximum  de- 
flection for  each  observation.  If  the  apparatus 
were  to  be  used  for  only  one  station,  the  wave- 
length of  which  is  fixed,  the  voltmeter  scale 
could  be  arranged  to  read  the  field  strength  di- 
rectly. 

In  the  case  of  3  LO,  the  following  field  strengths 
in  m/v  per  meter  were  found,  using  the  procedure 
outlined: 

DISTANCE  DIRECTION 


i  Mile 
5  Miles 
10  Mites 


North 
400 
90 


East 

350 
60 
30 


Wed 

200 

50 

25 


From  such  data  it  is  possible  to  draw  contour 
maps  of  the  field  pattern  of  a  station,  such  as 
those  secured  in  the  elaborate  investigation  of 
the  distribution  of  WEAF  and  WCAP  (Bown  and 
Gillett:  "Distribution  of  Radio  Waves  from 
Broadcasting  Stations  over  City  Districts," 
Proc.  1.  R.  E.,  Vol.  12,  No.  4,  August,  1924). 
Bown  and  Gillett  used  one  of  the  short-wave 
measuring  sets  developed  by  Bown,  Englund, 
and  Friis,  and  with  this  more  elaborate  apparatus 
were  able  to  get  down  to  field  strengths  of  the 
order  of  a  fraction  of  a  millivolt  per  meter; 
some  of  their  curves  extend  to  a  distance  of  over 
a  hundred  miles  from  the  transmitter.  The  simple 
apparatus  described  by  Cherry  is,  of  course, 
restricted  to  a  much  smaller  radius,  but  it  illus- 
trates the  principles  involved  just  as  effectively. 
The  contour  lines  in  the  case  of  3  LO  form  a  group 
of  quite  regular  concentric  ellipses,  which  would 
be  expected  with  the  transmitter  located  in  fairly 
open  country.  The  pattern  from  a  station 
located,  like  the  old  WEAF,  in  the  heart  of  a  city 
like  New  York,  is  far  more  irregular,  naturally. 

Within  the  radius  of  neglectable  absorption 
the  product  Ed  (field  strength  times  distance 
from  transmitter)  is  approximately  a  constant; 
this  relation  may  be  used  as  a  check  on  the  ac- 
curacy of  the  field  strength  measurements. 

Goldsmith    ("Reduction    of    Interference    in 
Broadcast  Reception,"  Proc.  I.  R.  E.,  Vol.  14, 
No.  5  October,  1926)  gives  the  following  table  of 
program  service  as  a  function  of  field  strength: 
SIGNAL  FIELD  STRENGTH  NATURE  OF  SERVICE 


10. 
loo. 

1000. 


volt  per  meter 
volts  per  meter 
volts  per  meter 
volts  per  meter 
volts  per  meter 


Poor  service 
Fair  service 
Very  good  service 
Excellent  service 
Extremely  strong 


Edgar  Felix  has  pointed  out  that  the  commercial 
value  of  a  broadcast  transmitter,  other  things 
being  equal,  is  a  function  of  field  distribution. 
This  is  true,  and,  when  the  owners  of  stations 
realize  it,  more  field  strength  measurements  will 
be  made  in  divers  neighborhoods.  If  the  field 
strength  is  not  being  produced  in  the  sections 
where  it  is  wanted,  the  artists  and  the  ad- 
vertisers might  as  well  go  home,  and  the  studio 
be  converted  into  a  salesroom  for  artificial 
flowers. 

The  limitations  of  space  will  not  permit  a 
longer  technical  discussion  of  the  subject. 
Readers  who  are  interested  beyond  this  point 
are  again  referred  to  Moullin's  book,  in  which 
Chapter  VIII  (pages  218-254)  's  devoted  to  a 
thorough  study. 


The  Listener's  Point  of  View 

HOW  CAN  GOOD  RADIO  PROGRAMS  BE  CREATED? 

By  JOHN  WALLACE 


IN  THIS  department  last  month  we  proposed 
the  question  "Can  the  Broadcaster  Improve 
Broadcasting?"    and    averred    that  in  our 
opinion  he  could  not  and  that  the  time  was  ripe 
for  him  to  call  in  outside  help.  The  suggestion  is 
a  sound  one  and  we  are  further  confirmed  in  our 
conviction  of  its  essential  truth  by  our  discovery 
that  the  same  idea  occurred,  at  almost  the  identi- 
cal time,  to  several  other  professional  reformers 
of  radio. 

Since  we  think  the  point  is  an  important  one 
and  worth  acting  upon,  and  since  it  is  best  em- 
phasized by  repeating  it,  we  quote  from  two  other 
scribes.  Mr.  Zeh  Bouck,  in  his  estimable  column 
in  the  New  York  Sun  said  in  part: 

"Our  asseveration  that  the  program  de- 
partments of  large  broadcasting  companies 
were,  in  principle  and  practice,  incapable 
of  turning  out  more  than  a  small  percentage 
of  meritorious  programs — originality,  inter- 
est, intelligence  and  esthetics  being  the  cri- 
teria of  merit — has  aroused  a  certain  amount 
of  controversial  interest.  The  question  arises, 
if  the  program  departments  of  the  large 
broadcasting  companies  should,  as  we  have 
suggested,  be  eliminated  in  some  relatively 
painless  manner,  who,  then,  should  prepare 
the  programs?  Or  rather,  let  us  say,  conceive 
the  programs,  for  the  actual  preparation,  the 
manual  labor,  could  still  be  left  to  the  studio 
hacks.  There  remain  three  possibilities.  The 
advertiser  can  prepare  his  own  programs, 
making  broadcasting  a  section  of  his  ad- 
vertising department.  Second,  the  advertis- 
ing agency  is  a  logical  consideration,  prepar- 
ing material  for  broadcasting  in  a  manner 
comparable  to  the  preparation  of  printed  ad- 
vertising. Both  of  these  systems  are  in  oper- 
ation to-day,  and  are  producing  programs 
notably  superior  to  the  rubber  stamp  variety 
turned  out  by  the  broadcast  organizations 
themselves.  .  .  . 

"On  the  other  hand,  the  program  depart- 
ment of  the  large  broadcasting  organization, 
turning  out  programs  by  the  hundreds,  fitting 
a  Swiss  cheese  classic  and  a  rather  extenuated 
ode  to  Persian  rugs  into  pretty  much  the 
same  skeleton  after  the  manner  of  Martin 
Eden  writing  his  pot  boilers,  necessarily  ex- 
hibits the  creative  talents  of  a  child  making 
mud  pies. 

"There  is  still  a  third  possibility  which  we 
originally  suggested  a  few  weeks  ago,  namely, 
the  purchase  by  the  broadcasting  company 
or  advertising  agency,  for  that  matter,  of 
ideas  and  radarios  submitted  by  free  lances, 
in  much  the  same  manner  that  stories  are 
submitted  and  bought  by  magazines.  In 
this  manner,  a  wealth  of  new  material  and 
ideas  would  supplement  the  rather  wornout 
traditions  of  radio  Cook's  tours  and  songs  of 
yesteryear. 

"These  ideas,  and  the  radarios  themselves 
when  necessary,  could  be  readily  adapted  to 
broadcasting  by  the  station  organization, 
which  is  often  as  adept  in  the  mechanics  of 
broadcasting  as  it  is  inept  in  creative  bril- 
liance." 

Mr.  Morris  Markey,  not  a  professional  ob- 
server of  radio,  but  a  writer  of  special  articles, 
leaped  immediately  to  this  same  conclusion  in  a 
story  written  recently  for  the  New  Yorker. 

"A  small  amount  of  work  is  being  done 
among  the  four  hundred  employes  of  the 
National  Broadcasting  Company  in  the  way 


of  experimental  programs.  There  have  been 
hesitant,  and  on  the  whole  unsuccessful,  efforts 
to  create  visual  images,  of  setting  and  atmos- 
phere, through  the  loud  speakers.  And  there 
have  been  sporadic  trials  of  dramatic  episodes, 
snatches  of  plays  and  such.  But  like  most  en- 
terprises organized  solely  for  the  pursuit  of 
money,  the  broadcasting  industry  is  con- 
servative. An  experiment  itself,  it  looks  upon 
experiment  in  the  entertainment  it  provides 
as  something  to  be  avoided.  It  has  failed  to 
recognize  that  radio  has  thus  far  produced 
not  one  suggestion  of  showmanship.  It  has 
failed  to  observe  that  the  showmanship  of 
the  microphone,  when  once  it  is  developed, 
will  be  a  vastly  different  thing  from  the 
showmanship  of  the  camera  or  the  stage. 
The  employes  whose  duty  it  is  to  keep  the 
performance  going  are,  in  the  large  part, 
hacks.  They  are  routine  men  who  are  not 
hired  for  imagination  or  invention,  but  for 
their  ability  to  fill  every  hour  on  the  air  with 
something  or  other,  preferably  of  a  revenue- 
producing  nature.  There  is  not  in  all  the  radio 
world  a  figure  comparable  to  the  producer 
in  the  theatre  or  the  director  in  the  movies — 
and  most  of  the  gods  of  the  trade  are  un- 
conscious, apparently,  of  their  need  for  such 
a  figure.  Vaguely  it  is  realized  that  something 
will  have  to  be  done  about  the  programs,  but 
few  in  the  industry  appear  to  understand 
that  these  programs  must  have  the  touch  of 
a  creative  person  upon  them." 

How  Long  Can  the  Ballyhoo  Last? 

THE    second    big    splurge    of    the   Dodge 
Brothers  Company,  its  much  touted  Movie 
Star  Hour  turned  out  to  be  "just  another 
program."  The  foregoing  review  is  a  decidedly 
unfair  one,  for  at  the  time  we  write,  the  program 
referred  to  has  not  yet  taken  place  and  will  not 
for  several  days.  It  is  to  be  made  up — or  at  the 
time  you  read  this,  was  made  up — of  the  voices 
of  Norma  Talmadge,  Charlie  Chaplin,  Douglas 
Fairbanks,  D.  W.  Griffith,  John  Barrymore,  and 


AMOS    N    ANDY;  ALIAS  CORRELL  AND 
GOSDEN 

The  former  "Sam  V  Henry"  team  so  popular 
with  listeners  to  WON  have  transferred  their 
attentions  to  the  microphone  of  WMAQ  of  Chi- 
cago where  they  are  heard  nightly  at  7:11  P.M. 
central  time,  except  Sunday  and  Wednesday 

104 


Dolores  del  Rio.  It  required  the  usual  million 
miles  or  so  of  telephone  wires,  the  conventional 
thousand  or  so  engineers,  and  of  course  the  tril- 
lion or  so  dollars  of  investment  and  commanded 
the  listening  attention  of  every  man,  woman, 
and  child  in  the  United  States  over  the  age  of 
thirteen  months.  And  it  served  to  convince  this 
particular  reviewer  that  most  of  the  individuals 
heard  had  selected  their  profession  with  great 
wisdom  and  ought  to  be  encouraged  to  stick 
to  the  silent  drama.  Mr.  Barrymore,  to  be  sure, 
contributed  an  excellent  reading  of  the  Hamlet 
soliloquy,  but  the  only  reward  for  listening  to 
the  others  was  a  satisfied  curiosity  concerning  the 
pitch  of  their  voices. 

Just  to  show  us  up  as  an  inaccurate  prognos- 
ticator,  that  program  may  turn  out  to  be  a  wow. 
But  it  hardly  seems  likely.  There  is  no  reason 
to  expect  that  because  Norma  Talmadge  is 
perfectly  entrancing  on  the  screen  her  voice  is 
going  to  prove  anything  in  our  parlor.  We 
would  be  far  more  willing  to  lay  a  wager  with 
Lloyd's  that  she  will  be  a  fizzle.  But  we  don't 
intend  to  write  indignant  letters  to  the  sponsor- 
ing company  arguing  this  point  for  they  are  just 
as  aware  of  it  as  we  are.  Our  opinion  of  their 
fancy  program,  and  indeed  the  opinions  of  any 
of  our  fellow  scribes,  mean  quite  nothing  at  all 
to  them.  And  rightly  so:  they  are  not  concerned 
with  devising  a  good  radio  program  but  with 
getting  something  up  to  ballyhoo.  They  have 
craftily  selected  six  of  the  biggest  names  in  the 
movie  world.  They  will  get  countless  miles  of 
newspaper  space,  probably  not  only  in  the  radio 
sections,  but  perhaps  in  the  movie  sections  as 
well,  and  even  in  the  news  columns  and  edi- 
torial pages.  In  other  words,  though  it  costs  them 
a  fortune  to  hire  the  movie  stars  and  the  broad- 
casting facilities,  they  will  probably  get  more 
newspaper  space  than  they  could  have  paid  for 
with  ten  times  the  sum,  and  they'll  get  the  air 
advertising  to  boot. 

Nobody,  not  even  the  querulous  critics,  actu- 
ally got  riled  about  their  thousand-dollar-a- 
minute  Victory  Hour;  we  were  all  too  bowled 
over  with  admiration  of  the  really  beautiful  ad- 
vertising coup  that  it  was.  But  nobody  pretends 
that  it  ranked  very  high  in  entertainment.  In  a 
"  list  of  the  best  programs  of  the  year  it  would 
have  placed  well  down  in  the  second  hundred. 
The  movie  star  hour  will  probably  take  even 
lower  rank. 

The  two  programs  mentioned  have  not  been 
the  only  Ballyhoo  Hours  in  radio's  history. 
Others  have  been  the  inaugural  hours  of  Palm- 
olive,  Wrigley  and  General  Motors.  Of  any 
Ballyhoo  Hour  this  is  true:  the  sponsor's  interest 
in  the  program  is  decidedly  secondary  to  his 
interest  in  the  printed  stuff  it  gives  him  a  chance 
to  cook  up  and  perchance,  to  have  published. 
In  other  words  the  program  is  no  end  in  itself 
but  merely  the  excuse  for  deluging  editor's  desks 
with  mimeographed  mouthings. 

In  some  ways  it  is  idle  for  us  to  rail  at  the 
Ballyhoo  Hour.  It  is  both  big  business  and  good 
business.  If  it  appears  to  exploit  the  sucker  strain 
in  the  Americano  the  answer  is  that  he  likes  to 
have  it  exploited.  But  as  a  gent  whose  waking 
hours  are  supposed  to  be  concerned  with  the 
vital  matter  of  seeing  radio  programs  improved 
it  is  our  bounden  duty  to  eye  such  stuff  aghast. 


JUNE,  1928 


THE  LISTENER'S  POINT  OF  VIEW 


105 


WE    DO   SOME    EYEING    AGHAST 

OUR  objection  to  the  Ballyhoo  Hour  is  pre- 
cisely, that,  while  it  doubtless  does  much 
good  for  the  advertiser,  it  does  nary  a  bit  of 
good  for  radio.  Furthermore  it  pains  our  frugal 
soul  to  see  so  much  mazuma  spent  in  such  a 
wasteful  way.  Wasteful,  as  far  as  radio  is  con- 
cerned, because  after  one  of  these  hours  is  over 
nothing  remains,  except  perhaps  an  unpleasant 
taste.  Nothing  has  been  contributed  to  the  "art " 
of  broadcasting,  no  new  precedent  has  been  es- 
tablished upon  which  bigger  and  better  develop- 
ments may  be  built.  Suppose  some  of  the  fifty  or 
so  thousand  dollars  that  is  commonly  planked 
down  for  one  of  these  programs  were  used  for 
the  employment  of  talented  persons  to  create 
something  new — such  as  the  Sound  Drama 
we  suggested  last  month — that  would  be  a 
real  step. 

But  such  arguments  can  carry  no  weight.  It  is 
too  much  to  ask  the  advertiser  to  worry  about  the 
future  of  the  radio  art.  We  shall  have  to  search 
another  point  of  attack.  Here's  one:  the  novelty 
of  these  Big  Splurge,  Ballyhoo  programs  can't 
last  forever.  Since  public  interest  in  them  is  at 
bottom  simply  curiosity  concerning  the  amount 
of  money  spent  and  the  magnitude  of  the  names 
employed,  each  succeeding  big  splurge  is  going 
to  have  to  outdo  its  predecessor  in  order  to  pique 
the  jaded  curiosity  of  that  public.  Eventually  it 
will  be  necessary  to  bill  the  crowned  heads  of 
Europe  and  transmit  the  stuff  over  jewelled 
platinum  wires  costing  $9.85  an  inch  in  order 
to  get  a  rise  out  of  the  radio  editors.  So  the 
Ballyhoo  Program  will  very  soon  exterminate 
itself. 

However,  there  is  still  another  reason  why  the 
commercial  broadcasters  themselves  ought  to 
take  steps  to  eliminate  the  ballyhoo  program 
and  that  is  that  it  doesn't  serve  to  increase  radio's 
prestige  very  much.  The  Big  Splurge  program 
attracts  what  the  storekeeper  knows  as  a  Bar- 
gain Day  Crowd.  The  merchant,  on  the  day  of  a 
big  sale,  lures  a  lot  of  strangers  into  his  store  who 
have  never  crossed  its  threshold  before.  Most  of 
them  never  will  again;  but  a  few  of  them  may 
observe  that  his  everyday  merchandise  is  of 
good  quality  and  may  become  habitual  custom- 
ers. 

The  Big  Splurge  program  sucks  in  perhaps  a 
couple  million  listeners  who  ordinarily  disdain 
radio,  refuse  to  purchase  receivers  and  are  only 
submitting  to  the  pleas  of  friends  to  "come  over 
and  play  a  hand  of  bridge  and  listen  to  Such  and 
Such."  This  is  a  swell  chance  to  corral  these  pros- 
pective customers  and  make  "em  come  back  for 
more.  But  the  Pomp  and  Circumstance  Program 
is  prone  to  have  one  or  other  of  the  two  following 
effects:  A.  The  program  turns  out  to  be  merely 
ordinary  as  entertainment,  thus  confirming  the 
transient  listener's  opinion  that  radio  is  a 
moron's  pastime  or;  B.  Great  musical  artists  are 
lavished  with  such  profusion  (as  in  some  Victor 
Hours)  that  his  follow-up  essay  at  listening  is 
dimmed  to  nothingness  by  contrast. 

A   Thursday  Evening  on  the  Blue 
Network 

PERHAPS   our  eternal   weeping   in    these 
columns  over  the  fact  that  radio  so  seldom 
attains  great  art,  and  so  frequently  suc- 
ceeds in  being  bad  art,  conveys  the  impression 
that  we  never  get  any  enjoyment  out  of  it  at  all. 
Not  so.  For  instance  last  night,  a  Thursday  eve- 
ning in  March: 

Arming  ourself  against  the  ordeal  with  an 
entertaining  novel,  we  plugged-in  KYW,  the  local 


vendor  of  the  Blue  Network's 
wares,  at  7:00  o'clock.  Central 
Time.  Well  we  didn't  get  in 
any  reading  during  the  first  half 
hour.  O.  Henry's  story,  "The 
Clarion  Call,"  was  being  presented 
in  the  "Re-Told  Tales"  series. 
Our  listening  was  mostly  a  matter 
of  conscientiousness  for  the  first 
ten  minutes,  but  after  that  the 
thing  carried  itself  along  for  the 
remainder  of  the  half  hour  and 
stacked  up  as  one  of  the  best 
radio  plays  we  have  heard.  A 
two-character  play,  making  use  of 
a  conventionally  far-fetched  O 
Henry  plot  it  was  "put  across"  by 
the  expectionally  fine  voice  acting 
of  the  villain.  Sorry  we  don't  re- 
member his  name;  the  good  job  of 
script  preparation  was  done  by  one 
Henry  Fisk  Carlton  and  the  pro- 
duction was  directed  by  a  Gerald 
Stopp. 

At  7:30  when  the  Ampico  Hour 
came  on  we  commenced  to  look  for 
our  place  in  our  book — for  we 
have  heard  some  rather  dismal 
Ampico  Hours.  But  unfortunately 
for  novel  reading  the  program 
opened  with  some  of  Smetana's 
music  for  "The  Bartered  Bride" 
which  we  like  too  much  to  miss. 
Then  Marguerite  Volavy,  playing  the  piano  both 
in  solo  and  in  concerto,  kept  our  willing  atten- 
tion for  the  rest  of  the  program. 

We  got  in  a  little  reading  during  the  Maxwell 
House  concert,  but  not  much.  This  program  is 
always  craftily  arranged  and  expertly  presented. 
The  "Old  Colonel  March"  and  the  "Indian 
Love  Lyrics"  we  could  have  got  along  very  nicely 
without,  but  Richard  Crooks  called  for  sitting 
up  and  taking  notice  when  he  sang  the  "Prize 
Song"  and  the  Siciliana  from  "Cavalleria." 
This  grand  singer — deservedly  popular — even 


AT  STATION  WGR,   BUFFALO 

Nancy  Cushman,  daughter  of  Howard  B.  Cushman,  director 

of  the  station,  confiding  to  the  world  that  she  is  two  years  old. 

"  M  icrophone  fright "  does  not  seem  to  bother  her 


put  beauty  in  the  banal  "Little  Bit  of  Heaven." 
The  orchestra  kindly  included  a  grand  waltz 
from  Komzak's  "  Bad'n  Mad'l'n." 

The  Continental's  program  followed  at  9:00 
o'clock.  This  hour,  too,  is  an  ever  reliable  one, 
made  up,  as  you  know,  of  opera  selections  and 
not  exclusively  of  the  hackneyed  ones.  However, 
as  two  hours  of  attentive  listening  is  enough  for 
anybody  to  put  in  consecutively,  we  at  this  point 
took  up  our  book  and  enjoyed  the  perfectly  swell 
radio  voices  of  Astrid  Fjelde,  Frederic  Baer,  et 
cie.,  as  a  rather  vague  background. 


THE    WBAL    ENSEMBLE 

This  group  is  heard  every  Friday  night  from  WBAL  Baltimore.  The  group  includes  (left  to  right): 
Michael  Weiner,  violinist-conductor;  Leroy  Evans,  pianist  and  Samuel  Maurice  Stern  'cellist.  Mi- 
chael Weiner  is  the  orchestral  supervisor.  WBAL  is  one  of  the  few  stations  that  takes  its  music  seriously 


SO  MANY  good  words  must  be  said  for  this 
month's  supply  of  records  that  we  feel  we 
ought  to  offer  a  word  of  explanation  at  the 
start.  Readers  grow  suspicious  when  any  reviewer 
waxes  consistently  eulogistic.  They  picture  all 
critics  as  mean  creatures,  shriveled  in  body  and 
soul,  who  starve  themselves  on  a  diet  of  vinegar 
and  sour  grapes  that  they  may  the  better  enjoy 
the  flaws  which  they  pick,  gloating  over  the  bones 
of  their  victims.  It  fills  us  with  joy  to  find  a  col- 
lection of  records  so  good  that  we  can  honestly  be 
lavish  with  praise.  Such  is  the  present  collection. 

Good  and  Popular 

In  the  Sing  Song  Sycamore  Tree  and  Four 
Walls  played  by  the  Ipana  Troubadours  directed, 
of  course,  by  S.  C.  Lanin  (Columbia).  What  is  so 
rare  as  a  really  good  tune?  Two  of  them,  of 
course.  And  here  they  are!  Superbly  played  by 
the  Troubadours  and  expertly  sung  by  Scrappy 
Lambert. 

The  Whip  and  We'll  Have  a  New  Home  in  the 
Morning  played  by  Nat  Shilkret  and  the  Victor 
Orchestra  (Victor).  Lyrics  that  are  different, 
harmony  that's  grand,  and  an  orchestra  that's 
infectious. 

Can't  Help  Lovin'  Dat  Man  and  Make-Believe 
played  by  Ben  Bernie  and  His  Hotel  Roosevelt 
Orchestra  (Brunswick).  Smooth — in  the  best 
Bernie  tradition,  and  with  Vaughn  De  Leath 
and  Scrappy  Lambert  doing  neat  vocalizing. 

Say  So!  and  Oh  Gee! — Oh  Joy!  played  by  Ben 
Selvin  and  His  Orchestra  (Columbia).  Yes,  and 
we'll  add  a  few  more  exclamation  marks  just  for 
good  measure!!!! 

Mary  Ann  and  //  /  Can't  Have  You  played 
by  Hal  Kemp  and  His  Orchesta  formerly  of 
the  University  of  North  Carolina.  (Brunswick). 
Where  they  got  their  M.  A.  (musical  acrobat) 
degrees,  no  doubt.  No?  Well,  they  got  very 
proficient  somewhere. 

Call  of  Broadway  and  Without  You  Sweetheart 
played  by  Vincent  Lopez  and  His  Casa  Lopez 
Orchestra  (Brunswick).  Mediocre  music  made 
more  than  a  little  danceable  by  a  swell  orchestra. 

Sensation  Stomp  and  Whiteman  Stomp  played 
by  Paul  Whiteman  and  His  Orchestra  (Victor). 
Whiteman  conducts  a  class  in  orchestral  gymnas- 
tics. Proving  what? 

Who  Gives  You  All  Your  Kisses  played  by  the 
Troubadours  (Victor).  As  usual  you  can  safely 
put  your  money  on  the  Troubadours.  They  will 
even  carry  the  weak  sister  on  the  other  side. 
What  Are  We  Waiting  For  played  by  Edwin  J. 
McEnelly's  Orchestra. 

Tin  Pan  Parade  played  by  the  Troubadours 
(Victor)  is  another  prize  winner;  Chloe,  on  the 
reverse,  by  the  All  Star  Orchestra  is  just  an  also- 
ran. 

Somebody  Lied  About  Me  and  Chloe  played 
by  the  Colonial  Club  Orchestra  (Brunswick). 
Something  old,  nothing  new,  something  bor- 
rowed, something  blue. 

I  Ol'  Man  River  and  Can't  Help  Lovin'  Dat  Man 
played  by  Don  Voorhees  and  His  Orchestra 
(Columbia).  Two  good  numbers  from  the  popu- 
lar Ziegfeld  musical  comedy,  "Show  Boat." 

My  Ohio  Home  and  Here  Comes  the  Showboat 
played  by  Jean  Goldkette  and  His  Orchestra. 
(Victor).  The  second  number  is  novel — and 
excellent. 

Rose  Room  and  Golden  Gate  by  Herb  Wiedoeft 
and  His  Orchestra  (Brunswick).  Musical 
publicity  for  the  Land  of  Sunshine. 

For  My  Baby  and  The  Man  I  Love  by  Leo 
Reisman  and  His  Orchestra  and  Fred  Rich  and 
His  Hotel  Astor  Orchestra,  respectively  (Colum- 
bia). F.  f.  f.  or  fine  for  foxtrotting. 

Tin  Pan  Parade  and  /  Told  Them  All  About 
You  sung  by  Ford  and  Glenn  (Columbia). 


The 

^Month's  New 
Phonograph 


Easily  the  best  of  the  recent  vocal  records. 

Sweetheart  of  Sigma  Chi  and  Charmaine  sung 
by  Allen  McQuhae  (Brunswick).  A  better  tenor 
voice  than  you  usually  hear  warbling  these  grand 
old  favorites! 

In  an  Oriental  Garden  and  Roses  for  Remem- 
brance played  by  the  Anglo-Persians  under  the 
direction  of  Louis  Katzman  (Brunswick).  Mr. 
Katzman  is  the  best  musical  gardener  we  know. 

Lolita  and  Yesterday  played  by  the  A.  and  P. 
Gypsies  under  the  direction  of  Harry  Horlick 
(Brunswick).  Very  nice  indeed. 

More  or  Less  Classic 

Lucia — Sextette  (Donizetti)  and  Rigoletto — 
Quartet  (Verdi).  (A)  sung  by  Galli-Curci,  Homer, 
Gigli,  De  Luca,  Pinza,  Bada;  (B)  sung  by  Galli- 
Curci,  Homer,  Gigli,  De  Luca  (Victor).  What's 
good  enough  for  Gatti-Casazza  is  good  enough 
fo'r  us. 

Song  of  the  Flea  (Moussorgsky)  and  Barbiere 
Di  Siviglia — La  Calunnia  (Rossini).  Sung  by 
Feodor  Chaliapin  (Victor).  The  name  of  this 
abysmal  basso  is  sufficient  guarantee  of  satis- 
faction on  any  record.  This  in  particular  is  de- 
lightful. 

Meistersinger-Kirchenchor  (Wagner)  and  Meis- 
tersinger-Wach'  auf!  Es  Nahet  Gen  Den  Tag 
(Wagner).  Sung  by  the  State  Opera  Chorus  of 
Berlin,  with  Orchestra,  conducted  by  Leo 
Blech  (Victor).  A  very  effective  imported  re- 
cording of  this  beautiful  choral  music  from 
Wagner's  merry  opera. 

Pagliacci-Son  Qua!  and  Pagliacci-Andiam! 
(Leoncavallo).  Sung  by  the  Metropolitan  Opera 
Chorus,  with  Metropolitan  Opera  House  Or- 
chestra, conducted  by  Giulio  Setti  (Victor). 
More  choral  music  that  is  worth  several  times 
the  price  of  admission. 

The  Masked  Ball— Is  It  Thou?  (Verdi)  and 
Pagliacci — Prologue  (Leoncavallo)  Sung  by 
Heinrich  Schlussnus  (Brunswick).  A  competent 
baritone  presents  these  two  operatic  selections. 

Andante  Canlabile  (Tschaikowsky)  and  Can- 
jonetta  (Tschaikowsky).  Played  by  Albert 
Spalding  (Brunswick).  Creating  one  paramount 
impression:  that  of  charming  grace. 

Chanson  Arabe  (Rimsky-KorsakofT — Kreisler) 
and  Le  Deluge  (Saint-Saens).  Played  by  Toscha 
Seidel  (Columbia).  Mr.  Seidel  is  assisted  in  the 
first  selection  by  Max  Rabinovitch  at  the  piano, 
and  in  the  second  by  Emanuel  Bay — because 
it  is  the  custom  and  not  because  this  talented 
violinist  needs  assistance. 

Ave  Maria  (Carnevali)  and  Stabat  Mater 
(Pergolesi).  Sung  by  Giuseppe  Danise  (Bruns- 
wick). A  rich  baritone  voice  lending  itself  very 
successfully  to  ecclesiastical  music.  The  ac- 
companiment of  chimes  in  the  Ave  Maria  is 
particularly  nice. 

Traviata — Prelude  (Verdi)  and  Sylvia  Ballet — 
Cortege  de  Bacchus  (Delibes).  Played  by  the 
Victor  Symphony  Orchestra  directed  by  Rosario 
Bourdon  (Victor).  No  home  is  complete  with- 

106 


out  these  familiar  but  none-the-less  lovely 
selections. 

Poet  and  Peasant  Overture,  Parts  I  and  2  (von 
Suppe).  Played  by  the  Brunswick  Concert  Or- 
chestra (Brunswick).  Part  i  is  the  dreamy  poet; 
part  2:  the  rollicking  peasant  .  .  .  but  you  know 
it;  it  has  appeared  on  every  "pop"  concert  pro- 
gram for  years. 

Emperor  Waltj  and  Wine,  Woman  and  Song 
Walt%  (Strauss).  By  Jacques  Jacobs'  Ensemble 
(Columbia).  Here  are  the  waltzes  of  yesteryear! 

Jolly  Fellows  Waltf  (Wollstedt)  and  The 
Skaters  (Waldteufel).  Played  by  the  Brunswick 
Concert  Orchestra  under  the  direction  of  Louis 
Katzman  (Brunswick).  Sweet  memories  of  the 
old  skating  rink  and  the  creaking  calliope!  The 
tunes  are  the  same,  that's  all! 

Recent  Album  Record  Sets 

WAGNER  BAYREUTH  FESTIVAL  RECORDINGS 
(Columbia).  In  one  album,  Masterworks  Set 
No.  79)  the  Columbia  Phonograph  Company 
offer  the  following  excerpts  from  four  Wagnerian 
operas:  (i)  Parsifal:  Transformation  Scene, 
Act  i ;  Grail  Scene,  Act  I ;  Flower  Maidens' 
Scene,  Act.  2;  Prelude,  Act  3;  and  Good  Friday 
Music,  Act  3;  (2)  Rheingold:  Entry  of  the  Gods 
into  Valhalla;  (3)  Die  Walkure:  Ride  of  the 
Valkyries:  (4)  Siegfried:  Forest  Murmurs,  Act  2; 
Prelude,  Act  3 ;  Fire  Music.  The  orchestra  is  that 
of  the  Bayreuth  Festival,  over  which  three  fa- 
mous conductors  share  the  honors  of  wielding  the 
baton.  They  are  Dr.  Karl  Muck,  one  time  direc- 
tor of  the  Boston  Symphony  Orchestra,  Siegfried 
Wagner,  and  Franz  von  Hoesslin.  The  recordings 
were  made  in  Bayreuth  during  actual  perform- 
ances of  the  operas  in  the  summer  of  1927  and 
have  been  approved  by  Siegfried  Wagner. 

We  will  not  go  into  a  detailed  description  of 
the  records.  You  either  know  and  love  the  music 
or  you  don't.  If  you  do,  you  will  want  the  album 
anyway.  If  you  don't,  you  should  get  the  album 
and  learn  to  know  the  music. 

The  set  contains  eleven  double-faced  records 
and  costs  J  16.50. 

Symphony  No.  4,  D  Minor,  (Op.  120)  by  Robert 
Schumann.  Played  by  the  New  Symphonic  Or- 
chestra, Berlin,  under  the  direction  of  Hans 
Pfitzner.  Complete  on  three  and  a  half  double- 
faced  records  (Brunswick). 

Schumann  conceived  the  Fourth  Symphony  as 
a  whole  rather  than  as  four  distinct  movements. 
The  same  thematic  material  runs  through  the 
entire  work.  The  symphony  is  very  colorful,  very 
warm  and  full  of  lovely  melodic  phrases.  The 
fourth  movement  is  particularly  beautiful. 

Concerto  for  Organ  and  Orchestra,  F  Major, 
(Op.  4,  No.  4)  by  George  Frederic  Handel. 
Played  by  Walter  Fischer  accompanied  by  or- 
chestra. Complete  on  two  double-faced  records. 
Concerto  for  Organ  and  Orchestra,  F  Major 
(Op.  777)  by  Joseph  Rheinberger.  Played  by 
Walter  Fischer  accompanied  by  orchestra.  Com- 
plete on  three  double-faced  records.  (Brunswick). 

The  Brunswick-Balke-Collender  Company 
would  have  acted  more  wisely  had  they  separa- 
ted these  two  concertos  rather  than  offered  them 
together  in  one  album.  The  Rheinberger  Con- 
certo, which  is  in  spots  uninteresting  to  the 
point  of  dullness  suffers  sadly  by  contrast  with 
the  exquisite  Handel  composition.  Both  con- 
certos are  beautifully  played  by  the  famous 
organist  of  the  Berlin  Cathedral. 

Death  and  Transfiguration  (Op.  24)  by  Richard 
Strauss,  played  by  the  State  Opera  Orchestra 
under  the  direction  of  the  composer.  Complete 
on  three  double-faced  records  (Brunswick). 

This  tone  poem  dealing  with  the  struggle  be- 
tween life  and  death  is  one  of  the  most  powerfully 
dramatic  of  modern  orchestral  compositions. 


"Radio  Broadcast's"  Directory  of  Vacuum  Tubes 


'PHE  table  below  is  as  complete  as  is  possible  to  make 
•*•  it  and  should  be  a  constantly  useful  reference  for  all 
radio  workers.  The  data  on  some  Western  Electric  tubes 
are  included  because  some  of  our  readers  live  in  Canada 
and  in  other  countries  where  tubes  of  this  manufacture 


are  available.  We  have  followed  the  RCA-Cunningham 
tube  terminology;  other  manufacturers  make  types  of 
tube  similar  in  each  class,  although  each  manufacturer 
has  his  own  terminology.  The  reader  who  desires  to  use 
a  CeCo  tube  for  example,  need  only  ask  his  dealer  or  the 


manufacturer  for  a  CeCo  of  the  201-A  type,  etc.  The 
same  follows  naturally  for  any  of  the  vacuum  tubes  in 
the  classifications  below  made  by  Arcturus,  Sovereign, 
Sylvania,  Marathon,  Gold  Seal,  Sonatron,  Kellogg, 
Magnetron,  Speed,  and  others. 


AVERAGE  CHARACTERISTICS  OF  RADIO  VACUUM  TUBES 

GENERAL 

DETECTION 

AMPLIFICATION 

MODEL 

USE 

CIRCUIT 
REQUIRE- 
MENTS 

INTER-ELECTRODE 
CAPACITIES  IN  MMFD. 
FILAMENT  COLD 

"A" 

SUPPLY 

FILAMENT!  FILAMENT 
TERMINAL]  CURRENT 

VOITAGE  IIAMPERES) 

DETECTOR 
GRID  RETURN 
LEAD  TO 

GRID 
LEAK 

MEGOHMS 

DETECTOR 
>'  BATTERY 
VOLTAGE 

DETECTOR 
PLATE  CURR'T 
MULIAMPERES) 

AMPLIFIER 
'B'BATTEKY 

VOLTAGE 

AMPLIFIER 
C"  BATTERY 
VOLTAGE 

AMPLIFIER 
PLATE  CURRENT 

(MILLIAMP£RES> 

A.C.PLATE 
RESISTANCE 

(OHMS) 

MUTUAL 
CONDUCTANCE 

MICROMHOS 

VOLTAGE 
AMPLIfl'TOfl 

FACTOR 

MAXIMUM 
UNDIS10RTED 
OUTPUT 

(MILLIWATTSI 

Ml 
WD-11 

Same  as  bel 

w,  except 

or  base 

which   1 

old    UV  ty| 

CX-12 
WX-12 

Detector  or 

Amplifier 

Transformer 

Coupling 

G-F6:G.P5.5;P.F7.5 

OrrC.llliV 
Storage  2  V 

1.1 

.25 

*F 

3  to  5 

22^1045 

1.5 

90 
135 

4^4 
lOfc 

2.5 
3.5 

15,500 
15,000 

425 
440 

6.6 
66 

7 
35 

CX-112A 
UX-1I2A 

Detector  or 

}  Amplifier 

Transformer 
Coupling 

G-F9;G-P11;  P-F7.5 

Storage  6  V 

5.0 

.25 

«F 

3  to  5 

45 

1.5 

90 
135 

V 

5.5 

7 

5.300 
5.000 

1,500 
1,600 

8 

a 

30 
120 

C-299 
UV.  199 

•M 

e    as   be 

iw,   except 

for  basi 

which   i 

old   UV  ty| 

1 

CX-299 
UX-199 

Detector  or 

Amplifier 

Transformer 

Coupling 

G-F  3.6;  GP3.5;  PF4.5 

OryCelUJV 
Stwigel  V. 

3:0 
3.3 

.060 
.063 

*F 

2  to  9 

45 

1 

90 

«i 

23 

15,500 

425 

6.6 

7 

CX-300A 
UX-200A 

Detector 

Tnr,sl.  or 

(esisCouptinj 

G-F  3  4;  G-P8.8;  P-F  1.5 

Storage  6  V 

5.0 

.25 

-.F 

2  to  3 

•    45 

1.5 

Following  UX-200  A  characteristics 
apply  only  for  Detector  connection 

30,000 

666 

20 

— 

ex-sou 

UX-201  t 

Detector  or 
Amplifier 

Transformer 
Coupling 

G-F5.8;  G-P10.1:  P-F  6.1 

Storage  6  V 

5.0 

.25 

+  F 

2to9 

45 

1.5 

90 
135 

V 

2.5 
3 

11,000 

10.000 

725 
800 

8 
8 

15 
55 

CX-  322 
UX-222 

Radio  Freq. 
»  Amplifier 

Special 
Shielding 

G-P  0.025 

SSSAl 

3.3 

.132 

— 

— 

— 

— 

135 

ij" 

1.5 

850,000 

350 

300  n 



CX-322 
UX-222 

Audio  Freq. 

(Amplifier 

Resistance 
Coupling 



Dr,l.«U'iV 
Stout.  «V 

3.3 

.132 

— 

- 

- 

— 

180} 

li° 

.3 

160,000 

400 

60 

— 

UX-226 
CX-  326 

Amplifier 
A.C.  Filament 
Type 

Transformer 
Coupling 

G-F3.65;  G-P8.2;  P-F  2.1 

Tnnsformff 

1.5V. 

1.5 

1.05 

'      - 

-    - 

— 

— 

90 
135 
180 

6 
Jl 

3.5 
6 
T5 

9,400 
7.400 
7,000 

875 
1.100 
1.170 

8.2 

8.2 
8.2 

20 
70 

160 

C-327 
UY-227 

Detector  A.C. 
Heater  Type 

Transformer 
Coupling 

G-F3.6;  S-P3.7:  P-F2.75 

Transformer 
2.5V. 

2.5  H 

1.75 

K 

2-9 

ti 

45 
90 

2 

7 

Following  UT-227C 
apply  on  y  for  Detec 

haracterietics 
or  connection 

10,000 
8,000 

800 
l.OOO 

8 
8 

— 

CX-340 
UX-240 

Detector  or 

Amplifier 

Resistance 
Coupling 

G-F3.4;  G-P  8.8;  P-F  1.5 

Storage  6V 

5.6 

.25 

*F 

2  to  5 

1351 
180! 

"0.3 

g 

135  I 
180? 

? 

.2 
.2 

150,000 
150.000 

200 
200 

30 

30 

— 

CX-112A 
UX-112* 

I    Power     ' 
'  Amplifier 

No  LS.C. 
Required 

G-F9;  G-P  11;  P-F  7.5 

Trlnslwmtr 
5*. 

5.0 

.25 

— 

— 

— 

— 

135 
1575 

10} 

7 
9.5 

5.000 
4,700 

1.600 
1700 

8 
8 

120 
195 

CX-220 
UX-120 

Power 

Amplifier 

No  L.S.C. 
Required 

G-F4.5;  G-P5.4;  PF4.4 

OrrCtlMlV. 
StorijH  V. 

3.0 
3.3 

.125 
.132 

— 

— 

—    ' 

'— 

135 

22^ 

6.5 

6,300 

525 

3.3 

110 

CX-371  A 
UX-171  A 

Power 
Amplifier 

LS.C. 

;wr 

G-F  6.8;  G  P  9.5;  P-F  6.5 

Stouj*  6  V. 

Tunsfuimfr 
5V. 

5.0 

.25 

— 

- 

— 

— 

£ 

180 

'M 

40  j 

10 
16 
20 

2.500 
2,200 
2,000 

1,200 
1,360 
1,500 

3.0 
3.0 
3.0 

130 
330 
700 

tX-310 
UX-210 

Power 
Amplifier 

LS.C. 

G-F  7;  G  P  8;  P-F  7 

Transformer 

;sv 

7.5 

1.25 

— 

— 

— 

— 

18, 
fg 
» 

I 

6.0OO 
5,'000 

i:4318 

1.550 
1.600 
1.600 

1 

Ijlo 

CX-350 
UX-250 

Power 
Amplifier 

LS.C. 

G-P  8.7 

Transforms 
7.5V. 

7.5 

1.25 

— 

— 

— 

— 

Jio1 

1! 

70 
84 

!! 

55 
55 

2,100 

i.eoo 

1 

3.8 

y 

43;iio° 

AVERAGI 

;  CHA 

RACTERISTICS 

DF  V 

r'ESTE 

RN  ELECTRI 

C  TUBES 

"N," 

215-A 

Detector  or 
Amplifier 

Transformer 
Coupling 

G-F  4.4;  G-P6;  P-F3.8 

— 

1.0 

0.25 

+  F 

2-9 

45 

1.0 

67 

6.0 

1.0 

20,000 

300 

6 

8 

"y" 

1020 

Amplifier 

Resis.  or 
Impedance 
Coupling 

— 

— 

2.0 

0.97 

— 

— 

— 

— 

130 

1.5 

075 

60.000 

500 

30 

4.2 

"L" 
216A 

Amplifier 

Transformer 
Coupling 

— 

— 

5-6 

1.0 

— 

— 

- 

— 

130 

9.0 

8.0 

6.000 

980 

5.9 

60 

"0" 
104  D 

Amplifier 

Transformer 
or  Imped. 
Coupling 

c,-rt.-i.G-r3.4(>,p-r&o 

— 

• 
4-3 

10 

— 

— 

— 

— 

130 

22  j 

20.0 

2,200 

1.100 

2.4 

145 

205  D 

Power 
Amplifier 

Transformer 
or  Imped. 
Coupling 

- 

4.5 

1.6 

— 

— 

— 

— 

350 

22.S 

33 

3,500 

2,000 

7 

890 

SPECIAL    PURPOSE    TUBES 

MODEL 

USE 

CIRCUIT 
REQUIREMENTS 

BASE 

MAXIMUM 
OVERALL 
HEIGHT 

MAXIMUM 
OVERALL 
DIAMETER 

PURPOSE 

CHARACTERISTICS 

CX-380 
UX-280 

Full  Wave 
Rectifier 

Full-Wave 
Circuit 

Large 
Standard 
UX  Base 

•r 

•A" 

Rectification  in 
Eliminators 

Filament  Terminal  Voltage..  5  Volts       > 
Filament  Current  2  Amperes  (R  M  g 
A.C.PIatt  Voltage  300  Volts   I 

(Max-per  Plate)                                        ' 

Max.D.C.Outpu 
D.C.Outpu 
oft 

Current  (both  Plates)                                                        125  Milltamperes 

Voltage  at  Max.  Current  as  applied  to  filter 
pica!  rectifier  circuit  260  Volts 

CX-  381 
UX-281 

Half  Wave 
Rectifier 

Half  or  Full 
Wave  Circuit 

Large 
Standard 
UX  Base 

•*• 

«" 

Rectification  in 
Eliminators 

Filament  Terminal  Voltage_,7.5  Volts  ^ 
Filament  Current  1.25  Amperes  \  R  M  S 
A.C.PI»t«  Voltage  750  Volts  j 
(Maximum) 

A.C.  Plate  V 
DC.  Output 
D.C.  Output 

oltage  

Rtcomminded          Minimum 
_  650..  750  Volts 

Current  

Voltage  as  applied  to  filter  of  typical  r 

ectifier  circuit.  .620.  .620  Volts 

CX-374 
UX-874 

Voltage 
Regulator 

Series 
Resistance 

Large 
Standard 
UX  Base 

•»" 

2ft" 

Constant 
Voltage 
Device 

yg^^^S^SS                           Operating  Vo,t.g.  90Vo,t,D.C. 
different  vaiuesofB-current                                  St.rt.ng  Voltage..  _125VoltsD.C. 
are  supplied                                                              Operating  Current  10-50  Milltamperes 

C-376 
UX-876 

Current 
Regulator 

(Ballast  Tube) 

Transformer 
Primary  of 
65  Volts 

iKiM. 

Standard 
Mogul  Type 
Screw  Base 

a" 

4" 

Constant 
Currant 
Device 

Designed  to  insure    onstant  input 

)per»ting  Current  1.7  Amperes 
Mean  Voltage  Drop  50  Volts 
Permissible  Variation....  tlOVolts 

despite  fluctuation    in  line  voltage 

C-386 
UX-886 

Current 
Regulator 
(BillaslTube 

Transformer 
Primary  of 
65  Volts 
for  use  on 
1  IS  Volt  Lin* 

Standard 
Mogul  Type 
Screw  Base 

a" 

2|V 

Con  start 
Current 
Device 

Designed  to  Insure    onstant  input                        Operating  Current  2.05  Amperes 
to  power  operated    adio  receivers                         Mean  Voltage  Drop  _  50  Volt* 
despite  fluctuation    In  line  voltage                       Permissible  Variation  1  10  Volts 

C-377 

Protective 
Tub. 

— 

Double  £ 
Contact 
Bayonet 
Auto.Typ« 

•A" 

•f 

Current 

Limiting 
Device 

Used  in'B'Battery  circuits  to 
prevent  excessive  current  resulting 
from  short-circuit  which  might 
damage  tubes  or  wiring 

Voltage  D 

rop  Across 

_    Half 
Filament 
2.5 
45 

FilanSa 
5       At  20  Mitliamperes  DC 
90        At90  Milliamperes  DC. 

t  U)  Note  Other  use  of  this  Radiotron  above'below) 
•    Inner  Grid  -I1/?  Volts,  Outer  Grid +  45  Volts.     0.15  Milliamperes 

0  Outer  Grid -l1^  Volts(  lnnerGrtd+22!^  Volts,6  Milliamperes 

1  Applied  thru  plate  coupling  resistance  of  250.0OO  Ohms 

A  Connection  to  shell  ol  base  for  third  terminal  which  is  the  lead 
to  mid-point  of  filament 


Note :  All  grid  voltages  are  given 
with  respect  to  cathode  or 
negative  filament  terminal 

Maximum  values  not  to 
be  exceeded 


Except  for  half  ampere  filament.UX-1 12  and  UX- 1 71  characteristics  are  identical  respectively  to  UX-1 12-A 

and  UX-171-A. 

K Cathode 

H HeaterVoltage 

LSC.. Loud  Speaker  Coupling,consisting  of  either  Choke  Coil  and  By-Pa&s  Condenser  or  Output  Transformer  oll'l 

orstep  down  ratio.recom mended  wherever  plate  current  (aC-)exceeds  lOmilliamperes. 
M With  a  screen-grid  tube, on  account  of  circuit  I  imitations, the  actual  voltage  amplification  obtainable  does 

not  bear  as  high  a  relation  to  the  voltage  amplification  factor  as  in  the  case  of  three  element  tubes. 


107 


Manufacturers'  Booklets 

A  Varied  List  of  Books  Pertaining  to  Radio  and  Allied 
Subjects  Obtainable  Free  With  the  Accompanying  Coupon 


12  E  A  DERS  may  obtain  any  of  the  booklets  listed  below  by  use- 
ing  tbe  coupon  printed  on  this  Page.  Order  by  number  only, 

1.  FILAMENT  CONTROL — Problems  of  filament  supply, 
voltage  regulation,  and  effect  on  various  circuits.  RADIALL 
COMPANY. 

2.  HARD  RUBBER  PANELS — Characteristics  and  proper- 
ties of  hard  rubber  as  used  in  radio,  with  suggestions  on 
how  to  "work"  it.  B.  F.  GOODRICH  RUBBER  COMPANY. 

3.  TRANSFORMERS— A  booklet  giving  data  on  input  and 
output  transformers.  PACENT  ELECTRIC  COMPANY. 

5.  CARBORUNDUM  IN  RADIO — A  book  giving  pertinent 
data  on  the  crystal  as  used  for  detection,  with  hook-ups, 
and  a  section  giving  information  on  the  use  of  resistors. 
THE  CARBORUNDUM  COMPANY. 

9.  VOLUME  CONTROL — A  leaflet  showing  circuits  for 
distortionless  control  of  volume.  CENTRAL  RADIO  LABORA- 
TORIES. 

10.  VARIABLE  RESISTANCE — As  used  in  various  circuits. 
CENTRAL  RADIO  LABORATORIES. 

12.  DISTORTION  AND  WHAT  CAUSES  IT — Hook-ups  of 
resistance-coupled  amplifiers  with  standard  circuits.  ALLEN- 
BRADLEY  COMPANY. 

1 5.  B-ELIMINATOR    AND    POWER    AMPLIFIER — Instruc- 
tions for  assembly  and  operation   using   Raytheon  tube. 
GENERAL  RADIO  COMPANY. 

153.  B-ELIMINATOR  AND  POWER  AMPLIFIER — Instruc- 
tions for  assembly  and  operation  using  an  R.  C.  A.  rectifier. 
GENERAL  RADIO  COMPANY. 

16.  VARIABLE  C9NpENSERS — A  description  of  the  func- 
tions and  characteristics  of  variable  condensers  with  curves 
and  specifications  for  their  application  to  complete  receivers. 
ALLEN  D.  CARDWELL  MANUFACTURING  COMPANY. 

17.  BAKELITE — A  description  of  various  uses  of  bakelite 
in  radio,  its  manufacture,  and  its  properties.   BAKELITE 
CORPORATION. 

21.  HIGH-FREQUENCY  DRIVER  AND  SH9RT-WAVE  WAVE- 
METER — Constructional  data  and  application.  BURGESS 
BATTERY  COMPANY. 

46.  AUDIO-FREQUENCY   CHOKES — A   pamphlet   showing 
positions  in  the  circuit  where  audio-frequency  chokes  may 
be  used.  SAMSON  ELECTRIC  COMPANY. 

47.  RADIO-FREQUENCY    CHOKES — Circuit    diagrams    il- 
lustrating the  use  of  chokes  to  keep  out  radio- frequency 
currents  from  definite  points.  SAMSON  ELECTRIC  COMPANY. 

48.  TRANSFORMER  AND  IMPEDANCE  DATA — Tables  giving 
the  mechanical  and  electrical  characteristics  of  transformers 
and  impedances,  together  with  a  short  description  of  their 
use  in  the  circuit.  SAMSON  ELECTRIC  COMPANY. 

49.  BYPASS  CONDENSERS — A  description  of  the  manu- 
facture of  bypass  and  filter  condensers.  LESLIE  F.  MUTER 
COMPANY. 

50.  AUDIO  MANUAL — Fifty  questions  which  are  often 
asked   regarding  audio  amplification,  and   their  answers. 
AMERTRAN  SALES  COMPANY,  INCORPORATED. 

51.  SHORT-WAVE  RECEIVER — Constructional  data  on  a 
receiver  which,  by  the  substitution  of  various  coils,  may  be 
made  to  tune  from  a  frequency  of  16,660  kc.  (18  meters)  to 
1999  kc.  (150  meters).  SILVER-MARSHALL,  INCORPORATED. 

52.  AUDIO  QUALITY — A  booklet  dealing  with  audio-fre- 
quency amplification  of  various  kinds  and  the  application 
to  well-known  circuits.  SILVER-MARSHALL.  INCORPORATED. 

56.  VARIABLE     CONDENSERS — A     bulletin     giving     an 
analysis  of  various  condensers  together  with  their  charac- 
teristics. GENERAL  RADIO  COMPANY. 

57.  FILTER   DATA — Facts  about  the  filtering  of  direct 
current  supplied  by  means  of  motor-generator  outfits  used 
with  transmitters.  ELECTRIC  SPECIALTY  COMPANY. 

59.  RESISTANCE  COUPLING^— A  booklet  giving  some 
general  information  on  the  subject  of  radio  and  the  applica- 
tion of  resistors  to  a  circuit.  DAVEN  RADIO  CORPORATION. 

63.  FIVE-TUBE  RECEIVER — Constructional  data  on 
building  a  receiver.  AERO  PRODUCTS,  INCORPORATED. 

70.  IMPROVING  THE  AUDIO  AMPLIFIER — Data  on  the 
characteristics  of  audio  transformers,  with  a  circuit  diagram 
showing  where  chokes,  resistors,  and  condensers  can  be  used. 
AMERICAN  TRANSFORMER  COMPANY. 

72.  PLATE  SUPPLY  SYSTEM — A  wiring  diagram  and  lay- 
out plan  for  a  plate  supply  system  to  be  used  with  a  power 
amplifier.  Complete  directions  for  wiring  are  given.  AMER- 
TRAN SALES  COMPANY. 

81.  BETTER  TUNING — A  booklet  giving  much  general  in- 
formation on  the  subject  of  radio  reception  with  specific  il- 
lustrations. Primarily  for  the  non-technical  home  construc- 
tor. BREMER-TULLY  MANUFACTURING  COMPANY. 

82.  SIX-TUBE  RECEIVER — A  booklet  containing  photo- 
graphs, instructions,  and  diagrams  for  building  a  six-tube 
shielded  receiver.  SILVER-MARSHALL,  INCORPORATED. 

83.  SOCKET  POWER  DEVICE — A  list  of  parts,  diagrams, 
and  templates  for  the  construction  and  assembly  of  socket 
power  devices.  JEFFERSON  ELECTRIC  MANUFACTURING  COM- 
PANY. 

84.  FIVE-TUBE   EQUAMATIC — Panel  layout,  circuit  dia- 
grams, and  instructions  for  building  a  five-tube  receiver,  to- 
gether with  data  on  the  operation  of  tuned  radio-frequency 
transformers  of  special  design.  KARAS  ELECTRIC  COMPANY. 

85.  FILTER — Data  on  a  high-capacity  electrolytic  con- 
denser used  in  filter  circuits  in  connection  with  A  socket 
power  supply  units,  are  given  in  a  pamphlet.  THE  ABOX 
COMPANY. 

86.  SHORT-WAVE  RECEIVER — A  booklet  containing  data 
on  a  short-wave  receiver  as  constructed  for  experimental 
purposes.    THE    ALLEN    D.    CARDWELL    MANUFACTURING 
CORPORATION. 

88.  SUPER-HETERODYNE  CONSTRUCTION — A  booklet  giv- 
ing full  instructions,  together  with  a  blueprint  and  necessary 
data,  for  building  an  eight-tube  receiver.  THE  GEORGE  W. 
WALKER  COMPANY. 


89.  SHORT-WAVE  TRANSMITTER — Data  and  blue  prints 
are  given  on  the  construction  of  a  short-wave  transmitter, 
together  with  operating  instructions,  methods  of  keying,  and 
other  pertinent  data.  RADIO  ENGINEERING  LABORATORIES. 

90.  IMPEDANCE  AMPLIFICATION — The  theory  and  practice 
of  a  special  type  of  dual-impedance  audio  amplification  are 
given.  ALDEN  MANUFACTURING  COMPANY. 

93;  B-SOCKET  POWER — A  booklet  giving  constructional 
details  of  a  socket-power  device  using  either  the  BH  or  313 
type  rectifier.  NATIONAL  COMPANY,  INCORPORATED. 

94.  POWER  AMPLIFIER — Constructional  data  and  wiring 
diagrams  of  a  power  amplifier  combined  with  a  B-supply 
unit  are  given.  NATIONAL  COMPANY,  INCPRPORATED. 

101.  USING  CHOKES — A  folder  with  circuit  diagrams  of 
the  more  popular  circuits  showing  where  choke  coils  may 
be  placed   to  produce  better    results.  SAMSON   ELECTRIC 
COMPANY. 

22.  A     PRIMER     OF     ELECTRICITY — Fundamentals     of 
electricity  with  special  reference  to  the  application  of  dry 
cells  to  radio  and  other  uses.  Constructional  data  on  buzzers, 
automatic  switches,  alarms,  etc.  NATIONAL  CARBON  COM- 
PANY. 

23.  AUTOMATIC    RELAY    CONNECTIONS — A    data    sheet 
showing  how  a  relay  may  be  used  to  control  A  and  B  cir- 
cuits. YAXLEY  MANUFACTURING  COMPANY. 

26.  DRY     CELLS     FOR     TRANSMITTERS — -Actual     tests 
given,  well  illustrated  with  curves  showing  exactly  what 
may  be  expected  of  this  type  of  B  power.  BURGESS  BATTERY 
COMPANY. 

27.  DRY-CELL  BATTERY  CAPACITIES  FOR  RADIO  TRANS- 
MITTERS— Characteristic  curves  and  data  on  discharge  tests. 
BURGESS  BATTERY  COMPANY. 

28.  B  BATTERY  LIFE — Battery  life  curves  with  general 
curves  on  tube  characteristics.  "BURGESS  BATTERY  COM- 
PANY. 

30.  TUBE  CHARACTERISTICS — A  data  sheet  giving  con- 
stants of  tubes.  C.  E.  MANUFACTURING  COMPANY. 

32.  METERS  FOR  RADIO — A  catalogue  of  meters  used  in 
radio,  with  diagrams.  BURTON-ROGERS  COMPANY. 

3^.  SWITCHBOARD  AND  PORTABLE  METERS — A  booklet 
giving  dimensions,  specifications,  and  shunts  used  with 
various  meters.  BURTON-ROGERS  COMPANY. 

35.  STORAGE      BATTERY      OPERATION — An     illustrated 
booklet  on  the  care  and  operation  of  the  storage  battery. 
GENERAL  LEAD  BATTERIES  COMPANY. 

36.  CHARGING  A  AND  B  BATTERIES — Various   ways   of 
connecting  up  batteries  for  charging  purposes.  WESTING- 
HOUSE  UNION  BATTERY  COMPANY. 

37.  WHY  RADIO  Is  BETTER  WITH  BATTERY  POWER — Ad- 
vice on  what  dry  cell  battery  to  use;  their  application  to 
radio,  with  wiring  diagrams.  NATIONAL  CARBON  COMPANY. 

53.  TUBE  REACTIVATOR— Information  on  the  care  of 
vacuum  tubes,  with  notes  on  how  and  when  they  should  be 
reactivated.  THE  STERLING  MANUFACTURING  COMPANY. 

69.  VACUUM  TUBES — A  booklet  giving  the  characteris- 
tics of  the  various  tube  types  with  a  short  description  of 
where  they  may  be  used  in  the  circuit.  RADIO  CORPORA- 
TION OF  AMERICA. 

87.  TUBE  TESTER — A  complete  description  of  how  to 
build  and  how  to  operate  a  tube  tester.  BURTON-ROGERS 
COMPANY. 

92.  RESISTORS  FOR  A.  C.  OPERATED  RECEIVERS — A 
booklet  giving  circuit  suggestions  for  building  a.  c.  operated 
receivers,  together  with  a  diagram  of  the  circuit  used  with 
the  new  4Oo-mil!iampere  rectifier  tube.  CARTER  RADIO 
COMPANY. 

102.  RADIO  POWER  BULLETINS — Circuit  diagrams,  theory 
constants,  and  trouble-shooting  hints  for  units  employing 
the  BH  or  B  rectifier  tubes.  RAYTHEON  MANUFACTURING 
COMPANY. 

103.  A.  C.  TUBES — The  design  and  operating  character- 
istics of  a  new  a.  c.  tube.  Five  circuit  diagrams  show  how 
to  convert  well-known  circuits.   SOVEREIGN   ELECTRIC  & 
MANUFACTURING  COMPANY. 

In  sending  the  coupon  below,  make  sure  that  your 
name  and  address  are  included  and  are  plainly 
written. 


USE  THIS  BOOKLET  COUPON 

RADIO  BROADCAST  SERVICE  DEPARTMENT 

RADIO  BROADCAST,  Garden  City,  N.  Y. 
Please  send  me  (at  no  expense)  the  following  book- 
lets indicated  by  numbers  in  the  published  list  above: 


Name. 
Address. 


(Number) 


(Street) 


(City) 


(State) 


ORDER  BY  NUMBER  ONLY 
This  coupon  must  accompany  every  request.  RB  6-28 


41.  BABY  RADIO  TRANSMITTER  OF  gxn-pEK  —  Descrip- 
tion and  circuit  diagrams  of  dry-cell  operated  transmitter. 
BURGESS  BATTERY  COMPANY. 

42.  ARCTIC  RADIO  EQUIPMENT  —  Description  and  circuit 
details   of  short-wave   receiver   and    transmitter   used    in 
Arctic  exploration.  BURGESS  BATTERY  COMPANY. 

58.  How  TO  SELECT  A  RECEIVER  —  A  commonsense 
booklet  describing  what  a  radio  set  is,  and  what  you  should 
expect  from  it,  in  language  that  any  one  can  understand. 
DAY-FAN  ELECTRIC  COMPANY. 

67.  WEATHER  FOR  RADIO  —  A  very  interesting  booklet 
on  the  relationship  between  weather  and  radio  reception, 
with  maps  and  data  on  forecasting  the  probable  results. 
TAYLOR  INSTRUMENT  COMPANIES. 

73.  RADIO  SIMPLIFIED  —  A  non-technical  booklet  giving 
pertinent  data  on  various  radio  subjects.  Of  especial  in- 
terest to  the  beginner  and  set  owner.  CROSLEY  RADIO  COR- 
PORATION. 

76.  RADIO  INSTRUMENTS  —  A  description  of  various 
meters  used  in  radio  and  electrical  circuits  together  with  a 
short  discussion  of  their  uses.  JEWELL  ELECTRICAL  IN- 
STRUMENT COMPANY. 

78.  ELECTRICAL  TROUBLES  —  A  pamphlet  describing 
the  use  of  electrical  testing  instruments  in  automotive  work 
combined  with  a  description  of  the  cadmium  test  for  stor- 
age batteries.  Of  interest  to  the  owner  of  storage  batteries. 
BURTON  ROGERS  COMPANY. 

95.  RESISTANCE  DATA  —  Successive  bulletins  regarding 
the  use  of  resistors  in  various  parts  of  the  radio  circuit. 
INTERNATIONAL  RESISTANCE  COMPANY. 

96.  VACUUM  TUBE  TESTING  —  A  booklet  giving  pertinent 
data  on  how  to  test  vacuum  tubes  with  special  reference  to 
a    tube   testing    unit.    JEWELL    ELECTRICAL    INSTRUMENT 
COMPANY. 

98.  COPPER  SHIELDING  —  A  booklet  giving  information 
on  the  use  of  shielding  in  radio  receivers,  with  notes  and 
diagrams  showing  how  it  may  be  applied  practically.  Of 
special  interest  to  the  home  constructor.  THE  COPPER  AND 
BRASS  RESEARCH  ASSOCIATION. 

99.  RADIO    CONVENIENCE    OUTLETS  —  A    folder   giving 
diagrams  and  specifications  for  installing  loud  speakers  in 
various  locations  at  some  distance  from  the  receiving  set. 
YAXLEY  MANUFACTURING  COMPANY. 

105.  COILS  —  Excellent  data  on  a  radio-frequency  coil 
with  constructional  information  on  six  broadcast  receivers, 
two  short-wave  receivers,  and  several  transmitting  circuits. 
AERO  PRODUCTS  COMPANY. 

106.  AUDIO    TRANsppRMER  —  Data    on    a    high-quality 
audio  transformer  with  circuits  for  use.  Also  useful  data  on 
detector  and  amplifier  tubes.  SANGAMO  ELECTRIC  COMPANY. 

108.  VACUUM  TUBES  —  Operating  characteristics  of  an 
a.c.  tube  with  curves  and  circuit  diagram  for  connection 
in  converting  various  receivers  to  a.c.  operation  with  a 
four-prong  a.c.  tube.  ARCTURUS  RADIO  COMPANY,. 

109.  RECEIVER  CONSTRUCTION  —  Constructional  data  on 
a   six-tube  receiver   using   restricted    field  coils.      BODINE 
ELECTRIC  COMPANY. 

no.  RECEIVER  CONSTRUCTION  —  Circuit  diagram  and 
constructional  information  for  building  a  five-tube  set 
using  restricted  field  coils.  BODINE  ELECTRIC  COMPANY. 

ill.  STORAGE  BATTERY  CARE—  Booklet  describing  the 
care  and  operation  of  the  storage  battery  in  the  home. 
MARKO  STORAGE  BATTERY  COMPANY. 

1  12.  HEAVY-DUTY  RESISTORS  —  Circuit  calculations  and 
data  on  receiving  and  transmitting  resistances  for  a  variety 
of  uses,  diagrams  for  popular  power  supply  circuits,  d.c.  resis- 
tors for  battery  charging  use.  WARD  LEONARD  ELECTRIC 
COMPANY. 

113.  CONE  LOUD  SPEAKERS  —  Technical  and  practical  in- 
formation on  electro-dynamic  and  permanent  magnet  type 
cone  loud  speakers.  THE  MAGNAVOX  COMPANY- 

114.  TUBE  ADAPTERS  —  Concise  information  concerning 
simplified  methods  of  including  various  power  tubes  in 
existing  receivers.  ALDEN  MANUFACTURING  COMPANY. 

115.  WHAT  SET  SHALL  I  BUILD?  —  Descriptive  matter, 
with  illustrations,  of  fourteen  popular  receivers  for  the  home 
constructor.  HERBERT  H.  FROST,  INCORPORATED. 

104.  OSCILLATION  CONTROL  WITH  THE  "PHASATROL"— 
Circuit  diagrams,  details  for  connection  in  circuit,  and 


,  , 

specific  operating  suggestions  for  using  the  "Phasatrol" 
as  a  balancing  device  to  control  oscillation. 
INCORPORATED. 


ELECTRAD, 


. 

1  16.  USING  A  B  POWER  UNIT  —  A  comprehensive  book- 
let detailing  the  use  of  a  B  power  unit.  Tables  of  voltages  — 
both  B  and  C  —  are  shown.  There  is  a  chapter  on  trouble- 
shooting. MODERN  ELECTRIC  MFG.  Co. 

117.  BEST  RESULTS  FROM  RADIO  TUBES  —  The  chapters 
are  entitled:  "Radio  Tubes,"  "Power  Tubes,"  "Super  De- 
tector Tubes,"  "A.  C.  Tubes,"  "Rectifier  Tubes,"  and 
"Installation."  GOLD  SEAL  ELECTRICAL  Co. 

118.  RADIO  INSTRUMENTS.  CIRCULAR  "J"  —  A  descriptive 
manual  on  the  use  of  measuring  instruments  for  :very  radio 
circuit  requirement.  A  complete  listing  of  models  for  trans- 
mitters, receivers,  set  servicing,  and  power  unit  control. 
WESTON  ELECTRICAL  INSTRUMENT  CORPORATION. 

120.  THE  RESEARCH  WORKER  —  A  monthly  bulletin  of  in- 
terest to  the  home  constructor.  A  typical  feature  article 
describes  the  construction  of  a  special  audio  amplifier  — 
AEROVOX  WIRELESS  CORPORATION. 

121.  FILTER  CONDENSERS  —  Some  practical  points  on  the 
manufacture  and  use  of  filter  condensers.  The  difference  be- 
tween inductive  and    non-inductive  condensers.  POLYMET 
MFG.  CORP. 

122.  RADIO  TUBES  —  Specifications  and  operating  charac- 
teristics of  vacuum  tubes.  Twenty-four  pages.  E.  T.  CUN- 
NINGHAM, INC. 

123.  B  SUPPLY  DEVICES  —  Circuit  diagrams,  characteris- 
tics, and  list  of  parts  for  nationally  known  power  supply 
units.  ELECTRAD,  INC. 

124.  POWER  AMPLIFIER  AND  B  SUPPLY  —  A  booklet  giving 
several  circuit  arrangements  and  constructional  information 
and  a  combined  B  supply  and  push-pull  audio  amplifier,  the 
latter  using  210  type  tubes.  THORDARSON  ELECTRIC  MFG.  Co. 

125.  A.   C.   TUBE  OPERATION  —  A  small    but    complete 
booklet  describing  a  method  of  filament  supply  for  a.c.  tubes. 
THORDARSON  ELECTRIC  MFG.  Co. 

126.  MICROMETRIC  RESISTANCE  —  How  to  use  resistances 
for:  Sensitivity  control;  oscillation  control;  volume  control; 
regeneration  control;  tone  control;  detector  plate  voltage 
control;  resistance  and  impedance  coupling:  loud  speaker 
control,  etc.  AMERICAN  MECHANICAL  LABORATORIES. 


1 08 


RADIO  BROADCAST  ADVERTISER 


109 


These  quality  instruments 
are  Thordarson  equipped: 


Buckingham 
MURDOCK 


£~7/)  iHEREVER  radio  apparatus  is  demon- 
\JL/  strated,  note  how  the  receivers  equipped 
with  Thordarson  Transformers  surpass  in  tonal 
reproduction. 

This  year,  more  than  ever  before,  fidelity  of 
reproduction  is  the  determining  feature  in  the 
sale  of  the  better  radio  apparatus.  Since  the 
musical  characteristics  of  a  radio  instrument 
depend  to  such  a  great  extent  on  a  wise  selec- 
tion of  the  audio  and  power  supply  transform- 
ers, it  is  significant  that  so  many  leading  man- 
ufacturers have  turned  to  Thordarson  as  the 
logical  transformer  source. 

Equally  significant  is  the  fact  that  not  once  since 
Thordarson  transformers  became  available  to  radio 
manufacturers  has  any  other  transformer  approached 
the  manufacturer  popularity  of  Thordarson. 

THORDARSON 

RADIO     TRANSFORMERS 


musical  performance 


{Thordarson   transformers   are  universally   available  to   custom  *»._ 
set  builders  as  well  as  manufacturers.  Wherever  radio  parts  are    jl 
sold,  there  you  will  find  a  complete  stock  of  Thordarson  Audio  -s^ 
and  Power  Supply  apparatus.   If  you  are  building  for  real  musical     j 
performance,  insist  on  Thordarson  Transformers.  ^ 

THORDARSON  ELECTRIC  MANUFACTURING  CO. 

Transformer  Specialists  Since  1895 

WORLDS  OLDEST  AND  LARGEST  EXCLUSIVE  TRANSFORMER  MAKERS 
C7turon  and  Kingsbun/ Streets      —  Chicaqo.Ill.USA.    s»i 


110 


RADIO  BROADCAST  ADVERTISER 


These  Men  Tell 
How  They  M.aKe 


'fldio- 


$350  a  Month 

"I  Feel  proud  of  my  success  in 
Radio  to  date.  My  profit  dur- 
ing the  last  two  months 
amounts  to  $700.  I  am  mak- 
ing good  and  I  have  not  fin- 
ished my  N.R.I,  course  yet. 
I  am  grateful  for  your  train- 
ing and  cooperation  to  date 
and  look  forward  to  still  big- 
ger success  when  I  graduate." 

Clarence  Heffelfuigt-i,  Temple,  Penna. 


$450  a  Month 

"I  want  to  say  a  few  words 
in  appreciation  of  the  bene- 
fits received  from  your  train- 
ing. In  addition  to  my  reg- 
ular work  in  what  I  believe 
to  be  the  largest  and  best 
equipped  Radio  Shop  in  the 
Southwest,  I  am  now  oper- 
ating KGFI.  I  am  proud  of 

j  the  fact  that  I  installed  and 

put  KGFI  on  the  air  witliom 

help    of    anyone    except    N.R.I.    I    am    averaging    #450 

per  month." 

Frank    M.  Jones,  922  Guadalupe  St.  San   Angelo,  Teias. 

I'll  Help  You  Become  a  Radio 
Expert 

Trained  men  are  needed  for  this  new 
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Radio"  tells  you  where  the  big  jobs  are  and  how 
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1  Will  Train  You  at  Home  in  Your  Spare  Time 

Two  months  from  now  you  can  be  making  $10, 
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This  64-Page  Book  FREE 

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•I.  E   Smith,  President 

.  6-0.  PUTIOML  MOID 


J.  E.  SMITH,  President 

Dept.  6-O,  National  Radio  Institute 

Washington,  D.  i'.. 

Dear  Mr.  Smith:  Send  me  a  copy  of  your  book  "Rich 
Rewards  in  Radio."  I  am  interested  in  getting  ahead 
and  want  to  know  all  about  Radio  money-making  op- 
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with  six  big  outfits  of  Radio  parts.  I  understand  this 
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Name    Age    

Address    

City    State    


The  Radio  Broadcast 

LABORATORY  INFORMATION 

SHEETS 


THE  RADIO  BROADCAST  Laboratory  Information  Sheets  are  a  regular  feature  of  this 
magazine  and  have  appeared  since  our  June,  1926,  issue.  They  cover  a  wide  range 
of  information  of  value  to  the  experimenter  and  to  the  technical  radio  man.  It  is  not  our 
purpose  always  to  include  new  information  but  to  present  concise  and  accurate  facts  in 
the  most  convenient  form.  The  sheets  are  arranged  so  that  they  may  be  cut  from  the 
magazine  and  preserved  for  constant  reference,  and  we  suggest  that  each  sheet  be  cut  out 
with  a  razor  blade  and  pasted  on  4"  x  6"  filing  cards,  or  in  a  notebook.  The  cards  should 
be  arranged  in  numerical  order.  In  July,  1927,  an  index  to  all  Sheets  appearing  up  to 
that  time  was  printed.  Last  month  we  printed  an  index  covering  the  sheets  published  from 
August,  1927,  to  May,  1928,  inclusive. 

All  of  the  1926  issues  of  RADIO  BROADCAST  are  out  of  print.  A  complete 
set  of  Sheets,  Nos.  I  to  88,  can  be  secured  from  the  Circulation  Department, 
Doubleday,  Doran  &  Company,  Inc.,  Garden  City,  New  York,  for  $1.00.  Orders  for  the 
next  set  following  can  also  be  sent.  Some  readers  have  asked  what  provision  is  made  to 
rectify  possible  errors  in  these  Sheets.  In  the  unfortunate  event  that  any  serious  errors  do 
occur,  a  new  Laboratory  Sheet  with  the  old  number  will  appear. 

— THE  EDITOR. 


No.  193 


RADIO  BROADCAST  Laboratory  Information  Sheet 


June,  1928 


'Motorboating" 


HOW  IT  CAN  BE  PREVENTED 


MANY  amplifiers  at  times  show  a  tendency  to 
"motorboat"  due  generally  to  interaction 
coupling  between  stages,  due  to  common  coupling 
in  the  plate-supply  unit.  This  effect  can  generally 
be  eliminated  by  using  the  circuit  shown  on  this 
Laboratory  Sheet.  This  circuit  was  suggested  in  a 
recent  bulletin  from  the  E.  T.  Cunningham  Com- 
pany. 

The  an  ti- motor  boa  ting  circuit  consists  of  a  net- 
work of  condensers  and  resistances  connected 
between  the  power  unit  and  the  B-plus  detector 
terminal  on  the  radio  receiver.  The  effect  of  this 
circuit  apparently  is  to  eliminate  coupling  effects 
at  the  low  frequencies  at  which  such  effects  are  most 
troublesome.  The  circuit  has  been  used  with  good 
results  in  the  Laboratory,  in  connection  with 
resistance -coupled  amplifiers  which  generally  show 
the  strongest  tendency  to  motorboat.  but  the  cir- 
cuit may  be  satisfactorily  used  with  any  type  of 
amplifier. 

It  is  not  difficult  to  add  this  circuit  to  any  existing 
receiver  installation.  To  do  this  it  is  simply  neces- 
sary to  connect  the  resistance  K  in  series  with  the 
lead  connecting  between  the  B-plus  detector 
terminal  on  the  receiver  and  the  B-plus  detector 


terminal  on  the  power 
unit.  One  2.0-mfd.  con- 
denser Ci  must  then 
be  connected  between 
the  B-plus  terminal 
and  the  B-minus  on 
the  receiver  and 
another  condenser  C> 
connected  between  the 
B-plus  detector  and 
minus  B  terminal  on 
the  power  unit.  It  is 
preferable  to  locate 
trhe  resistance  at  a 
point  close  to  the  re- 
ceiver rather  than  near 
the  power  unit. 

The  value  of  the  resis- 
tance depends  to  some 
extent  upon  the  char- 
acteristics of  the  receiver  and  the  power  unit. 
With  some  amplifiers  we  have  found  a  value 
of  10,000  ohms  to  be  satisfactory,  and  with  other 
amplifiers,  a  resistance  of  50,000~to  100,000  ohms 
was  required  to  prevent  motorboating.  A  value 
of  a.bout  50,000  ohms  seems  to  be  satisfactory  in 
most  cases. 


ftMlio  Recwver 

1 

8-  CWt 

>B 

HM 

— 

i-          B*Qet 

Power  Unit 

No.  194 


RADIO  BROADCAST  Laboratory  Information  Sheet 


June,  1928 


Push-Pull  Amplifiers 


HOWLING 


PUSH-PULL  type  amplifiers  in  many  cases 
exhibit  a  tendency  to  howl  at  some  audio  fre- 
quency due  to  feedback  through  the  interelectrode 
capacity  of  the  tubes.  When  this  occurs  it  is  obvi- 
ously impossible  to  obtain  satisfactory  operation 
from  the  amplifier.  The  howling  in  push-pull  ampli- 
fiers can  generally  be  readily  prevented  by  con- 
necting a  choke  coil  or  resistance  at  the  point 
marked  X  in  the  circuit  diagram.  When  construct- 
ing an  amplifier  of  this  type  it  is  wise  to  include  such 
a  choke  or  resistance  in  the  circuit;  no  by-pass 
condenser  should  be  placed  across  the  unit. 

The  inclusion  of  choke  or  resistance  in  this  circuit 
will  not  affect  the  quality  for  this  circuit  does  not 
have  to  carry  any  audio- frequency  currents.  In  some 
instances  it  will  be  found  necessary  to  prevent  howl- 
ing to  include  also  a  choke  coil  in  the  lead  from 
the  center  tap  of  the  output  transformer  and  the 
B-plus  terminal  ot  the  plate  supply. 

If  a  resistance  is  used  in  the  grid  circuit  it  should 
have  a  value  of  about  50,000  ohms.  Since  it  does 
not  have  to  carry  any  current,  any  ordinary  grid 
leak  type  of  resistance  unit  may  be  used.  The  chokes 
used  may  be  any  type  with  an  inductance  of  about 
10  henries  or  more.  The  primary  of  an  old  audio- 
frequency transformer  might  be  used  in  the  grid 
circuit  but  is  not  satisfactory  for  inclusion  in  the 
plate  circuit  between  the  center  tap  of  the  output 
transformer  and  the  plate  supply  for  when  con- 
nected at  this  point,  the  choke  must  carry  the  plate 
current  of  the  two  tubes,  which  may  be  enough  to 


burn  out  the  windings  of  an  ordinary  audio  trans- 
former. Use  at  this  point  some  device  designed  to 
carry  50  or  60  milliamperes.  The  circuit  given  on  this 
sheet  also  shows  the  use  of  a  resistance  Ri  to  supply 
C  bias  to  the  two  tubes.  Its  value,  depending  upon 
the  type  of  tubes  used,  is  given  below 

Type  of  Tube  Ri 

"112-A  750  ohms 

171-A  1000  ohms 

210  11 00  ohms 

Input 
Transformer 


RADIO  BROADCAST  ADVERTISER 


111 


Our  engineering  staff  •will 
gladly  cooperate  on  special 
condenser  problems  not 
covered  by  our  regular  pro- 
duction of  more  than  200 
types  of  units 


confidence  well 
placed       /     /     / 

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where  performance  must  uphold  the  manufacturer's  integrity, 
you  will  find  Faradon  Capacitors. 

It  has  been  demonstrated  that  Faradon  merits  acceptance  in 
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Control,  in  Marine  Direction  Finders— where  protection  of 
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there  you  will  find  Faradon,  the  electrostatic  condenser  of 
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112 


RADIO  BROADCAST  ADVERTISER 


The  Best 
Guarantee 

of  hidden  value  and  un- 
seen protection  in  a 
radio  tube  is  in  the  name 

Cunningham 

—a  reputation  for  qual- 
ity zealously  guarded 
for  thirteen  years. 

Manufactured  and  sold  under  rights,    patents 

and    inventions    owned    and/or  controlled    by 

Radio  Corporation  of  America 

E.  T.  CUNNINGHAM,  inc. 

New  York     Chicago     San  Francisco 


Since  1915 

k    Standard    ' 

.  for  all   / 

Sets 


No.  195 


RADIO  BROADCAST  Laboratory  Information  Sheet 


June,  1928 


A  Resistance-Coupled  Amplifier  With  Screen-Grid  Tubes 


CONSTRUCTIONAL    DATA 


February,  1927,  RADIO  BROADCAST  re- 
•*•  ported  some  experiments  made  in  the  Labora- 
tory on  the  use  of  the  screen-grid  tube  in  audio- 
frequency and  radio-  frequency  amplifiers,  and 
in  the  article  there  appeared  a  circuit  diagram 
of  a  resistance-coupled,  audio-  frequency  amplifier 
using  two  screen-grid  tubes.  Many  letters  have  been 
received  requesting  constructional  data  on  this 
amplifier  and  we  have  therefore  reprinted  the  cir- 
cuit diagram  on  Laboratory  Sheet  No.  196  and  the 
list  of  parts  necessary  to  construct  the  amplifier 
appears  at  the  end  of  this  Sheet. 

The  publication  of  this  circuit  diagram  and  list  of 
parts  should  not  be  taken  to  indicate  unqualified 
endorsement  of  the  amplifier  for  its  high  voltage 
gain  of  2200  (the  voltage  gain  of  an  average  two- 
stage  transformer  coupled  amplifier  is  250)  in 
some  cases  will  prove  more  of  a  disadvantage  rather 
than  an  advantage.  The  disadvantage  or  a  high 
gain  audio-frequency  amplifier  will  become  evident 
when  an  attempt  is  made  to  operate  it  from  a  B- 
power  unit.  When  an  ordinary  amplifier  is  used 
with  a  plate-supply  unit  which  provides  hum-free 
operation  no  difficulty  may  ensue;  but  when  this 
same  supply  is  connected  to  a  high-gain,  screen- 


grid  amplifier,  the  .hum  is  greatly  magnified  and 
may  be  of  entirely  too  high  a  value.  If  the  screen- 
grid  tubes  are  operated  from  batteries,  however, 
this  amplifier  will  give  very  satisfactory  results. 

To  construct  this  amplifier  the  following  parts  are 
necessary: 

Ri,  0.25-Megohm  Resistors 

/?s,  2.0-Megohm  Resistors 

/?:t,  20-Ohm  Filament  Resistors 

R\,  4-Ohm  Resistor 

/?s,  0.1 -Megohm  Resistor 

Ci,  0.01-Mfd.  Fixed  Condensers 

Cj,  4.0-Mfd.  Fixed  Condensers 

Cst  2.0-Mfd.  Bypass  Condensers 

Three  Sockets 

Binding  Posts 

No  special  care  is  required  in  the  construction  of 
this  amplifier  although  it  is  wise  to  arrange  the  lay- 
out so  that  the  various  grid  and  plate  leads  are 
short.  The  condensers  C»  and  the  resistor  R<,  are  in- 
corporated in  the  circuit  to  prevent  the  amplifier 
from  motorboating.  This  circuit  will  also  help  to 
keep  the  hum  low  if  the  device  is  operated  from  a  B- 
power  unit. 

A  frequency  characteristic  curve  of  this  amplifier 
made  in  this  Laboratory  showed  it  to  be  flat  from 
100  to  10,000  cycles. 


*    196  RADIO  BROADCAST  Laboratory  Information  Sheet  June,   1928 

Circuit  of  a  Resistance-Coupled  Screen-Grid  Amplifier 


+O     -O     +0     -O    +O 


C  Supply 


B         B+       B+       B+       B+ 
Pet.      45       135     Power^ 

6  Supply 


No.  197 


RADIO  BROADCAST  Laboratory  Information  Sheet 

Amplification.  Constant 


June,  1928 


HOW  IT  MAY  EASILY  BE  MEASURED 

IT  IS  not  difficult  with  simple  apparatus  to 
measure  the  amplification  constant  of  any  tube 
The  important  apparatus  required  to  make  such  a 
test  are  two  accurate  resistances,  one  variable,  the 
other  fixed,  and  a  milliammeter  capable  of  carrying 
the  normal  plate  current  of  the  tube  under  test. 
The  circuit  diagram  to  be  followed  in  making  this 
test  is  given  here.  The  following  parts  are  used  in 
the  circuit: 

EC — C-battery  with"  a  value  correct  for  the  tube 
under  test.  Eb — B-battery  with  a  value  correct  for 
the  tube  under  test.  Ea — Source  of  filament  voltage. 
E — 45  volt  B-battery.  Ri — Filament  rheostat.  Rs — 
Accurate  10-ohm  resistor.  Rj — Accurate  variable 
resistor,  having  a  maxmum  value  of  300  or  400  ohms. 
I  — Milliammeter  having  a  maximum  range  of 
about  20  milliamperes.  K  — Key  to  open  and  close 
the  circuit. 

The  important  resistor  in  this  circuit  is  Ri  which 
must  be  calibrated.  A  good  potentiometer  may  be 
used,  provided  it  is  supplied  with  a  dial  so  that  the 
amount  of  resistance  included  in  the  circuit  can  be 
calculated.  For  example,  if  the  potentiometer  has  a 
resistance  of  400  ohms  and  the  dial  reads  from  0  to 
100  then  each  degree  would  include  4  ohms. 

The  test  is  conducted  as  follows.  With  K  open, 
adjust  EC  and  Eb  so  that  the  tube  is  being  operated 
under  the  correct  conditions  of  grid  and  plate  volt- 
ege.  Note  the  plate  current  reading.  Now  depress 


K  and  note  the  change  in  the  reading  of  the  milliam- 
meter. Adjust  Ri  so  that  as  the  key  is  opened  and 
closed  no  change  takes  place  in  the  reading  of  the 
milliammeter.  When  resistor,  Ri,  has  been  adjusted 
so  that  the  plate  current  remains  constant,  cal- 
culate the  amount  of  resistance  at  Ri,  included  in 
the  circuit.  Divide  this  resistance  by  10,  the  value  of 
R>,  and  the  quotient  will  be  the  amplification  con- 
stant of  the  tube. 

EXAMPLE:  A  201  -A  type  tube  is  being  tested  and  a 
balance  is  obtained  when  there  are  83  ohms  in- 
cluded in  the  circuit  at  RI.  Dividing  Si  by  10  we 
get  8.3,  the  amplification  constant  of  the  tube. 


RADIO  BROADCAST  ADVERTISKR 


113 


Concentrated 
Effort! 


IN  specializing  on  and  perfecting  con- 
densers and  resistors  which  have  stood 
up  under  every  test  made  to  deter- 
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sively to  the  production  of  high  Quality 
condensers  and  resistors. 


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BROOKLYN,  N.  Y. 


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EVKRV  nth  in  RADIO  BROADCAST  appears  the  departments 
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after  placing  them  in  use,  find 
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GENERAL  RIDIO 

We  welcome  your  correspondence  in  regard*  to  technical  problems.    Bulletin 
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leading  set  manufacturers,  and  countless  thousands 
arc  in  use  in  home  built  sets.  Supplied  in  two  or 
three  terminal  type,  in  wide  range  of  resist  :nu  ix 
from  2,000  to  500,0x0  ohms,  and  with  or  without 
switch.  2  or  3  Terminal  Type,  less  switch,  $1.75. 
2  or  3  Terminal  Type-,  with  switch,  $2.10. 

HERBERT  II.  FROST,  INC. 

Main  O/icf.t  ami  Factory 

Elkhart.  In. I. 


114 


RADIO  BROADCAST  ADVERTISER 


A  New  A  C  Transformer 

with  terminals  for  use  with  all  types  of 

Wiring  Harnesses 

Here  is  the  latest  A  C  success  in  the  Dongan 
Approved  A  C  line  No.  6570,  built  into  a 
crystalized  lacquered  case,  is  equipped  with 
terminals  for  use  with  the  new  wiring  har- 
nesses. Designed  to  operate  with  4  UX  ia6, 
i  UY227  and  i  UX  171  power  amplifier  tubes. 
Also  equipped  with  lamp  cord  and  plug  out- 
let for  B-eiiminator  as  well  as  tap  for  control 
switch.  Price  $6.50. 

A  Complete  Line  of  Approved 

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Condensers 

for  Set  Manufacturers 
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The  reason  you  can  expect  real  engineering 
help  as  well  as  par  in  modern  design  and  con- 
struction is  due  to  the  fact  that  Dongan's  en- 
tire radio  business  always  has  been  devoted 
exclusively  to  the  interest  of  the  set  manu- 
facturer. 

Ask  for  information  and  prices,  on  any  de- 
sired type,  direct  from  Dongan  to  you. 

See  the  Dongan  Parts  Exhibit  at  the  R.  M.  A.  Show 

DONGAN  ELECTRIC  MFG.  CO. 

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V  '  TRANSFORMERS  of  MERIT  for  FIFTEEN  YEARS  . 


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For  Broadcasting,   Phonograph 

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THIS  transmitter  is  a  small  condenser  which 
varies  its  capacity  at  voice  frequency,  and 
is  coupled  direct  into  a  single  stage  of  ampli- 
fication, contained  in  the  cast  aluminum  case. 
The  output,  reduced  to  200  ohms,  couples 
to  the  usual  input  amplifier.  The  complete 
transmitter  may  be  mounted  on  the  regulation 
microphone  stand.  It  operates  on  180  v.  B  and 
6  or  12  v.  A  battery. 

This  transmitter  contains  no  carbon,  and  is 
entirely  free  from  background  noise.  Its  yearly 
upkeep  is  practically  nothing.  It  is  extremely 
rugged,  and  will  withstand  hard  usage. 

Price,  complete  with  20  ft.  shielded  cable, 
$225.00  F.O.B.  Chicago. 

J.  E.  JENKINS  &  S.  E.  ADAIR,  Engineer.* 

I.'.IMI  N.  Dearborn  Parkway, 

Chicago,  I '.  S.  A. 

Send  for  our  bulletins  on  Broadcasting 
Equipment 


No.    198  RADIO  BROADCAST  Laboratory  Information  Sheet  June,  1928 

The  Screen-Grid  Tube  as  an  R.  F.  Amplifier 


CALCULATING   GAIN 

T3ROBLEM: — Suppose  that  we  have  a  radio- 
*  frequency  amplifier  connected  as  indicated  in 
the  figure  and  that  a  screen-grid  tube  is  used.  How 
can  we  calculate  the  amplification  that  can  be 
obtained? 

SOLUTION: — To  solve  the  problem  we  must  make 
use  of  the  tube  constant  known  as  the  mutual 
conductance,  which,  for  the  screen-grid  tube,  has  a 
value  of  about  350  micromhos  or  0.000350  mhos. 
The  mutual  conductance  Gm  by  definition, 


where  Cm  is  the  mutual  conductance  in  mhos;  7»c 
is  the  alternating  current  flowing  in  the  plate  circuit; 
Eg  is  the  alternating  voltage  impressed  in  the 
grid;  transposing  this  equation  we  get 


across  the  input  Eg.  Transposing  equation  (4)  to 
get  this  ratio  we  obtain 
Et 


=  Gm  x  Z 


(5) 


This  equation  shows  that  the  gain  of  this  circuit 
using  a  screen-grid  tube  is  simply  equal  to  the 
mutual  conductance  of  the  tube  in  mhos,  times  the 
effective  impedance  of  the  tuned  circuit. 

Therefore,  if  we  know  the  impedance  into  which 
the  tube  is  working,  we  can,  by  multiplying  the 
impedance  by  Gm,  obtain  the  amplification.  If  the 
tuned  circuit  at  resonance  has  an  effective  imped- 
ance of  100,000  ohms  then  the  amplification  would 
be 

Amplification  =0.000350    X    100,000 
=35 


/ac  =  Gm  %  Es 


(2) 


The  voltage  Et  across  the  tuned  circuit  is  equal 
to  the  impedance  of  the  circuit  Z  times  the  current 
through  it  £t  -  /ac  x  Z  (3) 


and  therefore 


Et  =  Cm  x  Es  x  Z 


(4) 


The  amplification  of  the  circuit  is  equal  to  the 
voltage  across  the  output  Et  divided  by  the  voltage 


No.    199  RADIO  BROADCAST  Laboratory  Information  Sheet 

Current 


June,  1928 


ITS  DIRECTION   OF   FLOW 

THE  direction  of  flow  of  current  around  a 
*•  simple  circuit  consisting  of  a  battery  and  a 
resistance  is  generally  considered  to  be  as  indicated 
by  the  solid  arrows  in  sketch  A  on  this  sheet.  As 
indicated,  the  current  is  thought  of  as  flowing  put 
of  the  positive  terminal  of  the  battery,  through  the 
resistance  and  into  the  negative  terminal  of  the 
battery.  , 

Now  let  us  look  at  the  circuit  of  a  vacuum  tube, 
as  indicated  in  sketch  B.  In  this  circuit  we  would 
assume  that  the  current  would  flow  as  indicated  by 
the  solid  arrow,  i,  e.,  out  of  the  positive  terminal 
through  the  tube  and  into  the  negative  terminal 
just  as  it  did  in  circuit  A.  However,  we  know  that 
the  filament  of  the  tube  is  the  electron-emitting 
substance  and  that  the  electron  flow  is  from  the 
filament  to  the  plate.  Apparently  we  have  two 
currents  flowing  in  the  cir- 
cuit, and  this  has  led  some 
experimenters  to  believe 
that  there  were  two  distinct 
currents  flowing  in  the  cir- 
cuit, one  the  battery  current 
and  the  other  the  electron 
current.  This  is  not  so  and 

there  is  only  one  current         I «jT— 

flowing  in  the  circuit,  the 

electron  circuit.  (A) 


The  idea  that  the  elec- 
tric current  flows  from  the 
positive  to  the  negative 
originated  before  anything 
was  known  about  elec- 
trons. This  direction  of  (low 
has  since  been  proved 
to  be  wrong.  It  is  now 
realized  that  an  electric  cur- 
rent is  actually  a  flow  of 
electrons  and  that  elec- 
trons, being  negatively 
charged,  flow  toward  the 
point  of  positive  po- 
tential. Therefore  the  actual 
flow  of  current  in  the 
tube  circuit  B  and  the 
battery  circuit  A  is  as  in- 
dicated by  the  dotted  arrows. 

Fortunately  the  incorrect  assumption  that  was 
made  years  ago  for  the  direction  of  the  flow  of  cur- 
rent is  not  important  in  the  solution  of  electrical 
problems  so  long  as  we  remain  consistent  regarding 
the  direction  inlwhich  the  current  is  assumed  to  flow. 

Many  meters  used  in  electricity  are  marked 
with  plus  and  negative  signs  and  the  winding  of  the 
meter  is  arranged  so  that  the  pointer  on  the  meter 
will  deflect  in  the  right  direction  when  the  positive 
terminal  of  the  meter  is  connected  to  the  more 
positive  part  of  the  circuit. 


No.  200 


RADIO  BROADCAST  Laboratory  Information  Sheet  June,   1928 

Resistors 


DETERMINING    WHAT    SIZE   TO   USE 

TN  CHOOSING  a  resistance  for  any  particular 
•*•  purpose  it  is  necessary  to  determine  the  value 
required,  the  current  it  must  carry  and  then  from 
these  two  facts  determine  the  wattage  rating  re- 
quired. The  chart  published  on  this  sheet  will  prove 
useful  to  determine: 

(a)  the  wattage  rating  a  resistor  must  have  to 
carry  a  given  current 

(fr)  the  current  a  resistor,  of  given  wattage  rat- 
ing, will  carry 

The  curve  is  plotted  to  cover  resistors  up  to 
10,000  ohms  and  wattage  ratings  up  to  5  watts. 

EXAMPLE:  A  resistor  is  to  be  used  to  supply 
C-bias  to  a  171-A  type  tube.  The  plate  current  of  the 
tube  (which  must  flow  through  the  resistor)  is  20 
milliamperes.  The  required  C-bias  voltage  is  40 
volts.  What  value  of  resistance  and  what  wattage 
rating  should  the  resistor  have? 

To  calculate  the  required  value  of  resistance  we 
use  Ohm's  law. 


Referring  to  the  chart  below,  we  find  that  the 
vertical  line  corresponding  to  2000  ohms  crosses  the 
horizontal  line  corresponding  to  0.020  amperes 
(20  milliamperes)  at  the  point  indicated  between 
the  curves  of  1.0  and  0.25  watt  resistors.  In  such  a 
case  we  must,  of  course,  always  use  the  larger  size 
and  therefore  in  this  case  we  should  use  the  1.0- 
watt  resistor. 


Resistance 


_  Voltage 

"Current  in  amperes 

40 

~  0.020 
=  2000  ohms 


6000      8000      10.000   12,000  14,000  16,000 
RESISTANCE  IN  OHMS 


RADIO  BROADCAST  ADVERTISER 


115 


STATEMENT  OF  THE  OWNERSHIP.  MANAGE- 
MENT.  CIRCULATION,  ETC.,  required  by  the  Act 
of  Congress  of  August  24,  1912,  of  RADIO' BROAD- 
CAST, published  monthly  at  Garden  City,  New  York 
'or  April  1,  1928.  State  of  New  York,  County  of 
\assau. 

Before  me,  a  Notary  Public  in  and  for  the  State 
and  County  aforesaid,  personally  appeared  John  J. 
Hessian,  who,  having  been  duly  sworn  according  to 
law.  deposes  and  says  that  he  is  the  treasurer  of 
Doubleday,  Doran  &  Co.,  Inc.,  owners  of  Radio  Broad- 
cast and  that  the  following  is,  to  the  best  of  his 
knowledge  and  belief,  a  true  statement  of  the  owner- 
ship, management  (and  if  a  daily  paper,  the  circula- 
tion), etc..  of  the  aforesaid  publication  for  the  date 
shown  in  the  above  caption,  required  by  the  Act  of 
August  24,  1912,  embodied  in  section  411,  Postal 
Laws  and  Regulations,  printed  on  the  reverse  of  this 
form,  to  wit: 

1.  That  the  names  and  addresses  of  the  publisher, 
editor,    managing   editor,   and   business   managers   are: 
Publisher   Doubleday,  Doran  &  Co.,  Inc.,  Garden  City, 
N.    Y.;    Editor.    Willis    Wing,    Garden    City,    N.    Y.; 
Business    Managers,    Doubleday,    Doran    &    Co.,    Inc. 
Garden   City,   N.    Y. 

2.  That  the  owner  is:   (If  owned  by  a  corporation, 
its    name   and   address   must    be    stated   and    also   im- 
mediately   thereunder    the    names    and    addresses    of 
stockholders  owning  or  holding  one  per  cent,  or  more 
of   total   amount  of   stock.     If   not  owned   by   a   cor- 
poration,   the   names  and   addresses  of   the   individual 
owners  must  be  given.     If  owned  by  a  firm,  company, 
or   other    unincorporated   concern,    its    name    and    ad- 
dress,   as   well    as    those   of    each    individual    member, 
must    be    given.)     F.    N.    Doubleday,    Garden    City, 
N.    Y.;    Nelson    Doubleday,    Garden    City,    N.    Y . : 
S.   A.   Everitt,   Garden   City,  N.   Y.:    Russell   Double- 
day.    Garden    City,    N.    Y.;    George    H.    Doran,    244 
Madison  Avenue,  N.  Y.  C. ;   George   H.  Doran,  Trustee 
for   M.   N.   Doran,   244   Madison  Avenue,   N.   Y.    C. : 
lohn    J.    Hessian,    Garden    City,    N.    Y.;    Dorothy    D. 
Babcock,  Oyster  Bay,  N.  Y.:  Alice   De  Graff,   Oyster 
Bay    N.   Y.;    Florence  Van  Wyck   Doubleday,   Oyster 
Bay,  N.  Y. ;   F.  N.   Doubleday  or  Russell  Doubleday, 
Trustee  for  Florence  Doubleday,  Garden*  City,  N.  Y.; 
Janet  Doubleday,  Glen  Cove,  N.  Y.;  W.  Herbert  Eaton, 
Garden  City,  N.  Y.:  S.  A.  Everitt  or  John  J.  Hessian, 
Trustee   for  Josephine    Everitt.   Garden    Citv.    N.    Y.: 
William    |.    Neal.    Garden    City.    N.    Y.:    Daniel    W. 
\vc.  Garden  Citv,  N.  Y.;  E.  French  Strother,  Garden 
City     N.    Y  :    Henry    L.    Jones,    244    Madison    Ave., 
N     Y     C  :    W.    F.    Etherington,    50    East    42nd    St., 
N    Y    C.  :   Stanley   M.   Rinehart.  Jr.,    1192   Park  Ave., 
N.  Y.  C. 

3.  That    the    known    bondholders,    mortgagees,    and 
other  security   holders  owning  or   holding   I   per  cent. 
or    more    of    total    amount    of    bonds,    mortgages,    or 
other    securities   are:    (If   there   are    none,    so    state.) 
NONE. 

4.  That  the  two  paragraphs  next  above,  giving  the 
names  of  the  owners,  stockholders,  and  security  hold- 
ers, if  any,  contain   not  only  the  list  of  stockholders 
and   security   holders  as  they  appear  upon   the   books 
of   the  company   but  also,  in   cases  where  the  stock- 
holder or  security  holder  appears  upon   the  books  of 
the  company  as  trustee  or  in  any  other  fiduciary  re- 
lation,   the    name    of    the    person    or    corporation    for 
whom  such   trustee  is  acting,  is  given;    also   that   the 
said    two    paragraphs    contain     statements    embracing 
affiant's  full  knowledge  and   belief  as  to  the  circum- 
stances and  conditions  under  which   stockholders  and 
security   holders  who  do  not  appear  upon   the  books 
of  the  company  as  trustees,  hold  stock  and  securities 
in  a  capacity  other  than  that  of  a  bona  fide  owner; 
and    this    affiant    has   no    reason    to    believe    that    any 
other  person,  association,  or  corporation   has  any  in- 
terest direct  or  indirect  in   the  said  stock,   bonds,   or 
other  securities  than  as  so  stated  by  him. 

5.  That  the  average  number  of  copies  of  each  issue 
of    this   publication    sold   or   distributed,    through    the 
mails   or    otherwise,    to    paid    subscribers    during    the 

six  months  preceding  the  date  shown   above  is 

(This  information  is  required  from  daily  publications 

^Signed)     DOUBLEDAY,  DORAN  &  COMPANY,  INC. 

By  John  J.    Hessian,   Treasurer. 

Sworn  to  and  subscribed  before  me  this  15th  day  of 
March.  1928. 

[SEAL]  (.Signed)     Frank    0  Sullivan 

(My  commission  expires  March  30,    1928.) 

Why  not  subscribe  to  Radio  Broadcast?  By  the  year  only  $4.00; 
or  two  years  $6.00,  saving  $1.40.  Send  direct  to  DouhKlay, 
Doran  tf  Company,  Garden  City,  New  York. 


1010  .NVENTlOoVc 
*  WANTED    ^* 


en     >  new  b.ok 

__  >entions.     Oen'l 

Concentrate  oil  the   NEEDED 


The  world  needs  radii  inventions.  One  idea  may  make  yo 
ey  Raymond  F.  Tales  contains  a  list  ol  99  needed  Riidi 
s»nd  Imi,  and  etlort  in  worthless  inventions.  Cunceni 
inventions,  described  in  this  book. 

Mil  IITIIKK  NKEIIKII  1\\K\TIIINS 

ate  also  described,  mcludniq  tutomotiie.  Electrical.  tuto.  Meebanieel,  Chemi- 
cal.    Over  100  paqes.  durably  bound.     Send  no  meney.     Cut  out  this  odvor- 
tioement  and  send  it  to  us  with  your  name  and  address   plainly  written,  and 
yonr  copy  ot  this  remarkable  book  will  bo  sent  immediately,     ray  Ibe  pi 
moo  inly  t\.K  plus  postage  on  orrhral.     Neney  back  alter  10  days    ejantin 

olion    il    desired.     Limited  edition.     Write  NOW.       "If  I  •"•»'£• 

ea-h  with  oro>r.l     Bl  HKAl  OF  I.XVKNTIVK  STIKM'E,  Kf.pt.  4««, 


Do  You  Buy 
Satisfaction? 


Pattern  No.  139 

Higk  Rantancc  Voltmeter— For  the  Set 
Owner 


After  all,  it  is  the  satisfaction  you  expect  to  derive  from 
it  that  causes  you  to  buy  any  product.  It  may  be  satisfac- 
tion obtained  from  the  use  of  the  device,  or  satisfaction 
from  pride  of  ownership. 

Owners  of  the  Jewell  Pattern  No.  139  high  resistance 
voltmeter  for  the  set  owner  find  satisfaction  both  from  use 
and  pride  of  ownership,  for  the  use  of  this  instrument  brings 
assurance  of  accurate  results  and  its  appearance  will  be  an  attractive  addition  to  any  radio  set. 

Pattern  No.  139  is  of  the  D'Arsonval  moving  coil  type  with  high  internal  resistance  requiring 
little  current  draw,  with  results  much  more  accurate  than  obtained  with  the  ordinary  type  of 
voltmeter.  The  range  is  0-300  volts.  Movement  parts  are  all  silvered,  and  the  scale  is  silver 
etched  with  black  characters. 

Description  and  price  of  this  instrument  are  given  in  a  special  circular  No.  1 103.  Write  for  a  copy. 

Jewell  Electrical  Instrument  Company 

1650  Walnut  Street,  Chicago 

"28  Years  Making  Good  Instruments" 


Follow  the  Radio  Leaders! 


Those  who  know  the  value  of  microme 
resistance— precisely  matched  to  radio  a 
tions — always  specify  not  merely  variabl 
sistance  but — 


etric  \ 
ondi-  I 
le  re- 

TJ 


Ret;.  U.  S. 


ROBERT  S.  KRUSE 

Consultant  and  Technical  Writer 

103  Meadowbrook  Road,  West  Hartiord,  Conn. 
Hartford  4S32J 


Tlili  t>  a  gooJ  time  to  tukxrtkc  /or 

RADIO  BROADCAST 

Through  your  dealer  or  direct,  by  the  year  only  $4.00 


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The  Improved 

HAMMARLUND 
Equalizing  Condenser 

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the  previous  model. 

The  fixed  plate  of  brass,  the  mica 
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EVER  seeking  ways  to  better  its  products 
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But  quality  first  is  the  Hammarlund  ideal, 
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ammarjund 

PRODUCTS 


116 


RADIO  BROADCAST  ADVERTISER 


New  Aero  Circuits 

for  Either   Battery  or  A.  C.  Operation 

Proper  constants  for  A.  C.  operation  of  the  Im- 
proved Aero-Dyne  6  and  the  Aero  Seven  have  been 
studied  out,  and  these  excellent  circuits  are  now 
adaptable  to  either  A.  C.  or  battery  operation.  A.  C. 
blue  prints  are  packed  in  foundation  units.  They 
may  also  be  obtained  by  sending  250  for  each  direct 
to  the  factory. 


Aero  Universal 
Tuned  Radio  Frequency  Kit 

Especially  designed  for  the  Improved  Aero-Dyne  6. 
Kit  consists  of  4  twice-matched  units.  Adaptable  to 
2OI-A,  igp.  112,  and  the  new  240  and  A.  C.  Tubes. 
Tuning  range  below  200  to  above  550  meters. 

Code  No.  U-I6   (for  .0005  Cond.) $15.00 

Code  No.  U-163  (for  .00035  Cond.)  15.00 


Aero  Seven 
Tuned  Radio  Frequency  Kit 

Especially  designed  for  the  Aero  7.  Kit  consists 
of  3  twice-matched  units.  Coils  are  wound  on  Bake- 
lite  skeleton  forms,  assuring  a  95  per  cent,  air  dielec- 
tric. Tuning  range  from  below  200  to  above  550 
meters.  Adaptable  to  2io-A,  199,  112,  and  the  new 
240  and  A.  C.  Tubes. 

Code  No.  U-1Z  (for  .0005  Cond.) .  . .  $12.00 

Code  No.  U-1Z3  (for  .00035  Cond.) 12.00 

You  should  be  able  to  get  any  of  the  above 

Aero  Coils  and  parts  from  your  dealer. 

If  he  should  be  out  of  stock  order 

direct  from  the  factory. 

AERO  PRODUCTS,  INC. 

1772  Wilson  Ave.        Dept.  109       Chicago,  111. 


Radio 

Convenience 
Outlets 

Wire  your  home  for  radio.  These  out- 
lets fit  any  standard  switch  box.  Full 
instructions  with  each  outlet. 

No.  135— For  Loud  Speaker $1.00 

No.  137— For  Battery  Connections  2.50 
No.  136  For  Aerial  and  Ground  1.00 

With    Bakelite   Plates 

Now  furnished  with  a  rich  satin  brown  Bakelite 
plate,  with  beautiful  markings  to  harmonize,  at 
25  cents  extra.     See  Illustration. 
At  Your  Dealers 

Yaxley    Mfg.    Company 

Depl.  B,  9  So.  Clinton  Si. 

Chicago,   III. 


A-FILTER 

Here  is  a  new  kind 
of  DRY  and  HUM- 
LESS  A-FILTER, 
ready  to  hook  onto 
any  6  volt  charger, 
to  convert  your  fila- 
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No  harnesses,  no  new  tubes  required. 
Clip  this  ad,  and  send  with  your 
name  and  address  today  for  pam- 
phlet B-S. 

TORE   DEUTSCHMANN  CO. 

S  CAMBRIDGE,  MASS.  / 


The 


By  RAYMOND  TRAVERS 


LIFE  on  Teraina  (Washington  Island) 
was  one  of  complete  detachment  from  all 
the  rest  of  the  world.  After  a  thrilling 
ride  through  the  surf  and  a  safe  landing  on  the 
beach,  a  strange  sense  of  having  been  abandoned 
comes  over  you.  This  is  followed,  after  a  few  days 
by  a  feeling  of  emancipation.  At  last  life  is  freed 
from  its  great  complications,  and  the  mad 
existence  of  the  cities  is  but  a  hazy  thing  of  the 
past.  Living  is  simplified  to  the  fundamentals. 
Sleep  is  not  only  a  matter  of  the  nights  but  is 
indulged  in  during  the  hot  noon-day.  Food  comes 
from  cans  without  fuss  or  garnish.  Eating  is  a 
necessity — not  a  habit.  Everyone  has  work  to 
perform  and  in  so  doing  is  called  upon  to  exercise 
feats  of  ingenuity  beyond  belief.  There  isn't 
any  assistance  around  the  corner.  Further  and 
further  into  the  background  of  the  mind  fades 
the  worlds  beyond  the  horizon,  and  greater  be- 
comes the  content  with  the  life  at  hand. 

The  steamer  from  Honolulu  arrived  about 
every  four  months  (once  it  was  nine!)  and 
brought  mail,  excitement,  and  grief,  most  times. 
For  the  few  days  the  little  ship  lay  off  the  island, 
unloaded  its  cargo  of  food  and  supplies,  and  took 
aboard  the  tons  of  copra  we  had  laboriously  gath- 
ered, conditions  ashore  were  in  a  state  of  crazy 
confusion.  The  mail  had  to  be  sorted  for  matters 
of  great  importance  requiring  immediate  reply; 
the  supplies  to  be  checked  and  examined,  some 
to  be  returned  or  complained  about;  sometimes 
distinguished  guests  to  be  entertained,  when 
every  minute  was  so  vital  to  personal  affairs. 
At  last  the  sailing  hour  arrives,  the  ship  dis- 
appears, and  the  last  surf  boat  is  hauled  ashore. 
There  are  weary  sighs,  some  cursing,  a  few  drinks 
of  gin  and  cocoanut,  and  a  prayer  that  the 
blooming  ship  will  never  return! 

Tabueran  (Fanning  Island)  and  Teraina 
(Washington  Is- 
land), are  Brit- 
i  s  h  possessions, 
situated  one 
thousand  miles 
directly  south  of 
Honolulu,  about 
three  degrees 
north  of  the 
Equator,  and  five 
thousand  miles 
west  of  Panama. 
The  finest  copra 
in  the  world  is 
nutted  here,  but 
never  in  large 
quantities,  be- 
cause the  major 
parts  of  both 
islands  are  wild, 
prohibiting  maxi- 
mum crops  and 
efficient  collec- 
tion. In  1917  an 
Englishman  was 
sent  from  Londrn 
to  place  Washing- 
ton Island  on 
a  more  modern 
operating  basis 
and  increase  pro- 
duction. 

At  Fanning  is 
located  the  relay 
station  on  the 


ON  THE  sands  behind  the  coral  reefs  of 
Washington  Island,  in  the  Pacific  South 
Seas,  a  thousand  miles  south  of  Honolulu 
and  five  thousand  miles  west  of  Panama,  an  j 
audion  bulb  was  picked  up  some  years  ago.  j 
There  was  a  radio  telegraph  station  at  Wash-  j 
ington   Island,  and   R.  A.  Travers  was  the  1 
operator.  He  saw  the  audion  bulb,  recognized  j 
the   handiwork   of   the   inventor,   and    that  | 
night  put  the  bulb  in  the  mail,  with  the  fol-  j 
lowing  letter: 

WASHINGTON  ISLAND. 
VIA  HONOLULU  AND  FANNING  ISLAND 

December  i,  1919. 
Dr.  Lee  DeForest, 
New  York  City. 
Dear  Doctor  DeForest: 

I  am  sending  you  by  parcel  post  an  inter- 
esting valve  1  believe  to  be  one  of  you  pre-war 
1  types.  .  .  .  This  valve  traveled  many  miles  \ 
\  through  the   Pacific  ocean,   bobbed  over  a  | 
I  coral  reef,  and  came  to  rest  on  the  sands  of  J 
I  this  island.  . : .  Washington  island  is  a  wee  spot  ' 
|  in  the  wide  Pacific,  having  less  than  a  dozen 
1  miles  of  coast.  .  .  .  From  wreckage  picked  up 
I  from  time  to  time,  it  appears  drifting  objects 
I  come  from  the  eastward.  ...  I  believe  this  | 
I  valve  will  be  of  interest  in  your  collection. 
R.  A.  TRAVERS. 

The  foregoing  paragraphs  appeared  in  an 
article  in  the  November,  1025,  RADIO  BROAD- 
CAST as  introduction  to  part  of  the  history  of 
Dr.  Lee  DeForest.  Mr.  Travers  here  writes  his 
side  of  the  story  and  gives  an  interesting 
description  and  more  details  of  this  "wee 
spot  in  the  wide  Pacific"  where  the  "lost 
audion"  was  found. 


Pacific     Cable     Board's 


WASHINGTON    ISLAND    IN    THE    SOUTH    PACIFIC 

Here   the  author  found   the  audion   which 
had  drifted  thousands  of  mile's — from  where: 


Canadian-Australian 
lines.  The  cable 
from  Fanning  to 
Bamfield,  British 
Columbia,  is  the 
longest  in  the 
world,  running 
from  the  warm 
waters  of  the 
tropics  into  the 
slate  gray, 
choppy  and  cold 
shallows  of  the 
north — five  thou- 
sand miles!  All 
important  com- 
munications be- 
tween England 
and  the  Colonies 
were  routed  over 
this  cable,  and  so 
we  find  one  of  the 
notorious  Ger- 
man raiders  ter- 
rorizing the  Smith 
Pacific,  slipping 
ashore  at  Fan- 
ning, and  with 
some  well  placed 
dynamite,  en- 
larging the  area 
covered  by  the 
cable  buildings. 
Off-shore  the  ca- 
ble was  cut.  This 
may  have  had 


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THE  HAVEN  OF  A  SEA-GOING 
AUDION 

(continued  from  page  116) 

something  to  do  with  the  fact  that  in  May,  1917, 
I  left  San  Francisco  with  two  3  kw.  wireless 
sets  for  the  islands.  A  naval  operator  came  from 
Sydney  Navy  Yard  to  take  over  Fanning  and  I 
proceeded  to  Washington.  The  grief  and  struggle 
of  construction  is  another  tale. 

A  manager,  bookkeeper,  doctor,  surveyor,  two 
half-caste  overseers,  myself,  and  about  two- 
hundred  natives  set  about  building  a  settlement 
and  at  the  same  time  gathering  copra.  The 
replacing  of  thatched  huts  by  modern  cottages 
occupied  many  months  of  labor.  Every  Sunday 
morning  at  about  eleven  o'clock,  the  Staff 
assembled  and  in  a  very  dignified  manner  made 
an  inspection  of  all  work  and  of  the  native 
quarters.  To  the  manager  this  was  a  serious  affair 
executed  with  military  severity,  but  to  the  others 
it  was  a  joke,  and  much  playing  took  place 
behind  his  back.  A  match  on  the  floor  or  under 
a  native's  house  was  sufficient  to  have  the  offen- 
der arrested  and  brought  before  "Court"  Sunday 
evening.  Many  amusing  situations  developed 
in  "Court"  and  often  the  stern  manager-judge 
"lost  face".  There  was  the  case  of  Kabuta  who 
refused  to  clean  his  house  unless  he  was  paid 
overtime  for  so  doing.  He  contended  that,  as  the 
house  belonged  to  "The  Company"  he  should  be 
paid  for  keeping  it  clean.  This  brought  about  an 
impasse,  and  he  was  arbitrarily  ordered  to  polish 
it  up  if  he  expected  to  live  in  it.  The  following 
morning  native  police  reported  Kabuta  had  not 
slept  in  his  house  and  was  absent  from  camp. 
This  violated  two  more  rules.  Kabuta  stated  he 
had  spent  the  night  sleeping  on  boxes  of  dyna- 
mite in  a  lean-to,  about  a  mile  up  the  beach, 
where  cleaning  wasn't  necessary. 

DISCOVERING   THE    AUDION 

C\>->  THE  morning  of  September  16,  1917,  I 
^-^  experienced  the  same  sensation  as  the  man 
who  saw  the  giraffe  for  the  first  time  and  ex- 
claimed, "There  isn't  any  such  animal!"  The 
usual  inspection  was  in  progress,  and  the  average 
number  of  arrests  being  made,  when  my  atten- 
tion was  attracted  to  a  little  glass  ball  suspended 
from  the  rafters  in  a  native's  room.  Wrinkling 
my  nose  in  native  fashion  point,  I  asked  of  the 
fellow  squatting  on  the  floor,  "Terrah?"  He 
shrugged  his  shoulders  up  around  his  ears  and 
with  a  puzzled  expression  on  his  chocolate  fea- 
tures replied,  "Ungcome!"  1  extended  my  hand 
for  the  thing  and  he  passed  it  to  me.  Imagine 
my  astonishment  to  find  that  it  was  a  DeForest 
Audion,  the  first  I  had  ever  seen,  but  recognized 
from  pictures.  I  wanted  to  know  where  the 
native  had  found  it  and  he  said,  "Ay  naka  may 
en  tardy,"  ("  It  came  here  from  the  sea,")  He  had 
picked  it  up  while  walking  along  the  beach  and 
thought  it  a  pretty  bauble. 

There  is  a  native  custom  which  forces  one  to 
give  up  an  object  if  the  other  party  desiring 
it  merely  begs  for  it  saying,  "Now!  Ye  pacheco." 
In  this  manner  I  became  the  owner  of  the  tube, 
one  of  the  strangest  and  most  fragile  bits  ever 
cast  ashore  by  the  pounding  seas. 

Remember  that  this  was  in  1917  and  1  doubt  if 
there  was  a  handful  of  these  tubes  in  the  entire 
territory  contiguous  to  the  Pacific  Ocean.  Some 
tubular  shaped  Audiotrons,  made  in  Berkeley, 
California,  were  being  used.  I  had  a  dozen  myself. 

The  question  as  to  where  this  Audion  could 
have  come  from  was  a  difficult  one  to  answer. 
Teraina  was  900  miles  from  the  Australian  sea- 
lanes  and  1800  miles  from  the  courses  to  Tahiti 
Honolulu  was  the  nearest  port  and  that  was  a 

(continue*.!  on  fmge  ;;6') 


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THE  HAVEN  OF  A  SEA-GOING 
AUDION 

(continued  from  page  7/7) 

thousand  miles  to  the  north'ard.  Allowing  a  drift 
of  but  a  few  miles  a  day,  many  months  must 
have  passed  and  miles  unwound  from  the  point 
of  departure  until  riding  the  surf,  this  tiny  glass 
bulb  found  rest  on  the  sands  at  Teraina.  Study 
of  other  drift  material  offered  the  only  oppor- 
tunity for  conjecture. 

Cocoanuts  are  supposed  to  have  come  from 
Central  America  and  vegetated  throughout  the 
South  Pacific.  While  digging  an  irrigation  canal 
on  Washington  Island,  an  old  Manahikian  canoe 
was  found.  It  was  quite  a  distance  inland  from 
the  present  shore  of  the  lake  and  buried  in  gravel, 
which  undoubtedly  was  the  old  lagoon  beach, 
before  the  present  lake  was  formed  by  the  la- 
goon's closing.  The  bow  is  in  good  condition  and 
now  occupies  a  prominent  position  in  the  Bishop 
Museum,  Honolulu.  There  are  legends  told  by 
the  old  men  of  Manahiki,  about  travels  to  Te- 
raina in  great  canoes.  One  tale  recites  how  the 
King  of  Manahiki,  angered  at  some  of  his  people 
who  refused  to  return  from  Teraina,  cursed  them 
and  cried  for  a  tidal  wave  to  wipe  out  the  rebel 
village.  The  canoe  is  pointed  out  as  evidence  of 
Manahikian  occupation  and  the  closed  lagoon  as 
the  fulfillment  of  the  curse. 

Of  more  recent  date  is  a  load  of  lumber  con- 
signed to  A.  P.  McDonald,  Tahiti.  This  must 
have  been  washed  overboard  from  some  schooner 
and  found  its  way  to  Fanning  and  Washington. 
Fanning  is  75  miles  to  the  southeast  of  Washing- 
ton. The  lighter  pieces  came  ashore  at  Washing- 
ton while  all  the  great,  heavy  beams  piled  up  on 
Fanning,  without  exception.  The  British  Com- 
missioner at  Fanning  seized  the  lumber  for  his 
new  house,  quoting  a  law  some  hundreds  of  years 
old,  which  claims  everything  from  the  sea  for  the 
Crown. 

Standard  Oil  Barge  No.  95  almost  foundered 
off  the  coast  of  lower  California.  Everything  on 
deck  was  swept  away.  A  year  and  a  half  later, 
one  of  her  steel  lifeboats,  buoyed  by  the  airtight 
compartments  in  bow  and  stern,  majestically 
floated  past  our  island.  An  object  resembling  a 
human  head  was  visible,  silhouetted  against  the 
bright  noon-day  sky.  Dave  Greig,  the  overseer, 
and  I  were  the.  only  ones  at  the  settlement,  ex- 
cept the  cooks  and  store  boys.  Greig  launched 
a  small  fishing  boat  and  started  to  run  down  the 
visitor.  What  suspense  as  I  stood  on  the  beach 
and  watched  him  overtake  the  lifeboat!  Then  he 
gave  me  the  prearranged  signal  that  there  wasn't 
any  one  aboard.  After  quite  a  struggle  against 
the  strong  current,  Grieg  succeeded  in  bringing 
the  boat  ashore.  We  were  surprised  to  find  it 
nearly  full  of  water  and  with  a  great  many  fish 
of  all  sizes  swimming  about.  The  bottom  was 
filled  with  fish  bones,  who  had  perhaps  served  as 
food  for  later  comers.  Many  of  the  bones  were 
from  large  sharks.  This  craft  must  have  come 
at  least  5000  miles,  and  as  it  is  highly  improbable 
that  it  traveled  anything  like  a  straight  course, 
the  distance  must  have  been  many  times  that. 

All  of  this  drift  has  been  from  the  eastward  and 
in  each  case,  except  the  audion,  a  point  of  origin 
is  known.  It  is  possible  that  the  DeForest  wan- 
derer started  somewhere  in  the  Atlantic,  bobbed 
through  the  Canal,  crossed  the  Pacific,  and  came 
to  rest,  at  last,  on  the  beach  at  Teraina.  This  is 
not  any  more  difficult  to  believe,  than  the  mere 
fact  that  it  came  out  of  the  sea,  over  a  rocky  reef, 
to  the  beach — a  beach  whose  entire  length  is  but 
eleven  miles,  situated  in  mid-Pacific  where  dis- 
tances are  measured  in  thousands  of  miles! 

The  cocoanuts,  the  canoe,  the  lumber,  the  life- 
boat, and  the  DeForest  Audion — symbols  of  an 
age,  and  slender  threads  from  other  worlds — 
to  peaceful,  detached  Teraina! 


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leading  set  manufacturers,  and  countless  thousands 
are  in  use  in  home  built  sets.  Supplied  in  two  or 
three  terminal  type,  in  wide  range  of  resistances 
from  2,000  to  500.000  ohms,  and  with  or  without 
switch.  2  or  3  Terminal  Type,  less  switch,  $1.75. 
2  or  3  Terminal  Type,  with  switch,  $2.10. 

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Main  Offices  and  Factory 
Elkhart.  Ind. 


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THE  new  Aero  "International  Four"  Receiver  marks  a  distinct  milestone  in 
radio  progress. 
For  the  first  time,  radio  frequency  amplification  on  short  waves  has  become  a 
possibility.     Sensitivity  has  been  increased,  control  has  been  made  far  easier  and   re- 
ceiver noises  have  been  reduced  considerably  below  their  former  level  by  development 
in  the  design  of  this  receiver. 

Newly  designed  parts  have  been  incorporated  throughout.  The  tuning  condenser  has 
no  mctal-on-metal  bearing,  so  that  the  hissing  noises  formed  by  the  variation  in  contact 
has  been  eliminated.  New  coils  of  a  smaller  diameter,  having  a  much  smaller  external 
field,  a  better  shape  factor  and  improved  efficiency  are  employed.  The  foundation 
unit  with  holes  drilled  for  mounting  every  part,  simplifies  the  construction  of  the  set, 
and  assures  proper  placement  of  the  parts.  The  isolation  of  the  antenna  from  the 
tuned  stage  means  that  swinging  of  the  antenna  will  have  no  effect  on  tuning  and 
variations  in  antenna  lengths  have  little  effect  on  the  operation  of  the  set. 

The  Aero  "International  Four"  is  to  our  knowledge  the  first  short  wave  receiver  of 
any  kind  designed  peculiarly  for  reception  of  musical  broadcast  rather  than  code  re- 
ception, and  as  such  fills  its  place  far  better  than  the  best  of  all-purpose  outfits,  al- 
though due  to  its  ease  of  control  and  great  sensitivity,  it  is  superior  to  most  all  perfect 
short  wave  sets  in  any  field. 

Uses  The  Aero  Coil  L.  W.  T.  10  Kit 

The  new  kit  of  coils  illustrated  above  is  the  L.  W.  T.  10,  price  $10.50.  This  kit  is 
designed  to  go  with  special  drilled  and  engraved  foundation  unit,  in  which  mounting 
base  is  provided  in  drilled  sub-panel.  If  you  desire  to  furnish  your  own  foundation 
unit,  order  the  L.W.T.  II  Kit,  price  $11.50.  This  kit  includes  mounting  base. 

The  New  Aero  L.  W.  T.  12  Coils 

This  is  the  new  Aero  L.  W.  T.  12  kit. 
Consists  of  3  new  small  diameter  Aero 
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son's coils.  You  should  own  this  kit  if 
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national Four  direct  from  our  factory.  Write  us  today  for  descriptive  literature,  list 
of  parts,  and  special  price  list.  You'll  want  to  build  and  own  this  dandy  receiver. 
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Dept.  109  1772  Wilson  Ave.  Chicago,  111. 


Published    monthly.       Vol.     XIII.     Nn.     :;.       Published     at    Garden    Cii>      N. 
Garden  City.    N.    Y.,    as    sccuiul  class  mail    mutter.      Douhioda.v.    Uoran  & 


Subscription    price    14.00    a    year.       Entered    at    the    post    office    at 
ni'aiiv.    Inc..    Garden   City,    N     V 


RADIO  BROADCAST 


JULY,  1928 


WILLIS  KINGSLEY  WING,  Editor 

KEITH  HENNEY  EDGAR  H.  FELIX 

Director  of  the  Laboratory  Contributing  Editor 


Vol.  XIII.  No.  3 


Cover  Design    -  -    From  a  Design  by  Harvey  Hopkins  Dunn 

Frontispiece     A  Giant  Radio' Equipped  British  Passenger  Airplane  124 

What  Hope  for  Real  Television?       R.  P.  Clarion  125 

The  March  of  Radio  *      An  Editorial  Interpretation  129 


Aviation  Must  Come  to  the  Use  of  Radio 
No  Innovations  or  Revolutions  for  1928 
Broadcast  Regulation  at  a  Standstill 
The  Inequalities  of  "Equalization" 
Another  Non-Radio  Man  for  the  Commission 


The  Commission  Eliminates  Its  First  Station 
The  Engineers'  Plan  of  Allocation 
The  High -Frequency  Spectrum 
Recent  Radio  Events 


A  New  Principle  in  Audio  Transformer  Design    Kendall    Clough 
"Radio  Broadcast's"  Home  Study  Sheets  -     - 


No.  i.  The  Nature  of  Radio  and  Electricity 


No.  2.  Determining  the  Capacity  and  Induct- 
ance of  a  Radio  Circuit 


Making  an  A-Power  Unit  From  Your  Battery  Charger 

Robert  Burnhatn 

New  Apparatus  »'*-*-  Useful  Information  on  J\[ew  Products 
A  Good  Amplifier-Power  Unit  for  the  250  Tube  Howard  Barclay 
"Strays"  from  the  Laboratory  Keith  Henney 


New  Crystal  Control 

Prices  of  British  "Components" 

Present  Interesting  Trends  in  Radio 

Radio  Gossip 

Publications  Worthy  of  Note 

"Skim  Milk  Masquerades  as  Cream" 


133 
135 


137 
139 
141 

143 


Technical  Smoke  Screen 

Recent  Interesting  Technical  Articles 

Present  Compression  Type  Resistors 

From  a  Lab  Circuit  Fan 

Who  Our  Readers  Are 

A  Flux  for  Nichrome  Wire 


An  Interesting  A-B-C  Power  Unit  and  One-Stage  Amplifier 

/.  George  Uzmann 

A  Universal  Set  and  Tube  Tester    •'*'-.'•      D.  A.  R.  Messenger 
Broadcast  Station  Calls  with  a  Past  -  •    William  Fenwic\ 

"Our  Readers  Suggest" 


Checking  Power  Unit  Voltages 
A  Convenient  Telephone  Jack  Arrangement 
Neutralizing  the  Short- Wave  Amplifier 
Wave  Trap  Tuned  Antenna  Combination 


Additional     Amplification     for     Phonograph 

Pick-Up 
To  Stop  That  Whistling 


As  the  Broadcaster  Sees  It  • 

Note  on  Programs 


D«ign  and  Operation  of  Broadcast  Stations 
21.  Water-Cooled  Vacuum  Tubes 


A  Space-Charge  Amplifier  and  B  Supply 
A  Fine  Program  You  Will  Never  Hear 


H.  P.  Manly 

John  Wallace 


The  Listener's  Point  of  View 


A  Receiver  for  Short- Wave  Broadcast  Reception     Bert  E.  Smith 
Manufacturers'  Booklets     *    - 

"Radio  Broadcast's"  Laboratory  Information  Sheets    -     - 


No.  201.  Tube  Life 

No.  aoa.  Farm  Lighting  Systems 

No.  103.  Tuned  Circuits 

No.  204.  Line  Voltage  Variations 

No.  205.  Electrical  Measuring  Instruments 


No.  206.  A  Screen-Grid  Resistance-Coupled 
Amplifier 

No.  207.  Equalizing  Wire  Lines  for  Broad- 
casting 

No.  208.  Power  Values  in  Radio  Receiving 
Antennas 


Letters  from  Readers 


145 
148 
150 
151 


A  Short'Wave  Adapter  for  the  R.B.  Lab  Receiver  Hugh  S.  Knowles  153 

How  to  Build  a  Beat'Frequency  Oscillator     -          G.  F.  Lampkin  156 
"Radio    Broadcast's"    Service    Data    Sheets    on    Manufactured 

Receivers 159 

No.  3.  The  Grebe  A.C.  Six  No.  4.  The  Kolster  6  K  A.  C. 


Carl  Dreher     161 


163 

165 

167 

170 
174 


179 


OTHER  THINGS. 


The  contents  of  this  magazine  is  indexed  in  The  Readers*  Guide 
to  Periodical  Literature,  which  is  on  file  at  all  public  libraries. 


MANY  favorable  comments  have  been  received  about  the 
list  of  stations  throughout  the  world  transmitting  below 
loo  meters  which  occupied  three  pages  of  our  May,  1928,  issue. 
Although  this  list  was  very  carefully  checked  for  accuracy 
against  the  best  lists  of  stations  we  could  find,  some  errors 
undoubtedly  crept  in.  Some  of  our  readers  have  been  kind 
enough  to  send  us  information  which  should  be  included  when 
the  list  is  published  again  in  RADIO  BROADCAST.  In  the  course  of 
the  next  four  or  five  months  we  shall  reprint  the  list,  com- 
pletely revised.  We  urge  our  readers  to  help  us  by  sending  in 
any  corrections  which  should  be  included  at  that  time. 

IN  THIS  issue  we  begin  a  new  feature,  "RADIO  BROADCAST'S 
Home  Study  Sheets"  prepared  by  Keith  Henney,  director 
of  the  Laboratory.  Back  in  September,  1925,  Mr.  Henney's 
first  article,  "New  Fields  for  the  Home  Experimenter"  under- 
took to  lead  the  radio  experimenter  who  had  tired  of  merely 
building  radio  sets  and  who  desired  to  learn  more  about  what 
makes  the  wheels  go  'round.  Since  that  time,  many  articles  of  a 
similar  nature  have  been  published  in  these  pages.  With  this 
issue  we  begin  the  "Home  Study  Sheets,"  which  are  arranged 
so  that  the  interested  readers  can  remove  them  with  a  razor 
blade  and  keep  a  complete  file.  The  Sheets  to  follow  will  contain 
a  great  deal  of  practical  information  in  what  we  believe  is  the 
most  useful  form.  We  shall  be  glad  to  have  our  readers'  opinions 
on  the  innovation.  It  is  a  policy  of  RADIO  BROADCAST  to  print 
as  much  useful  information  as  possible  with  due  thought  to  the 
form  in  which  it  is  presented.  The  "Lab  Sheets"  —  the  2o8th 
appears  in  this  issue  —  were  the  first  in  this  series.  Next  follow 
the  "Service  Data  Sheets  on  Manfactured  Receivers"  and  we 
have  now  added  the  "Home  Study  Sheets."  Still  other  ser- 
vices, similarly  valuable,  are  in  prospect. 

UNLESS  we  are  greatly  mistaken,  several  of  the  articles  in 
this  issue  are  going  to  excite  a  great  deal  of  interest.  The 
leading  article  by  R.  P.  Clarkson,  "What  Hope  for  Real  Tele- 
vision7" attempts  to  explain  television  systems  in  general  and 
to  point  out  what  now  seems  to  be  the  only  possibility  of  suc- 
cess. 

OUR  August  issue  will  contain,  among  other  things,  a 
description  of  the  d.c.  operated  "Lab"  circuit,  another 
timely  article  on  television,  a  really  fine  article  by  David  Grimes 
on  phonograph  pick-up  units,  a  constructional  and  operation 
article  on  the  Cooley  Rayfoto  system,  first  introduced  to  our 
readers  in  our  September,  1927,  issue,  a  story  on  a  new  short- 
wave receiver,  and  the  first  article  of  a  series  by  Robert  S.  Kruse. 
Mr.  Kruse  for  a  number  of  years  was  technical  editor  of  S^ST. 
His  first  article  deals  with  the  mystery  of  5-meter  work  and 
will  be  of  especial  interest  to  all  our  amateur  friends  who  read 
RADIO  BROADCAST.  All  the  regular  features  will  appear  in  our 
August  issue  as  well. 

AS  THIS  issue  goes  to  press,  a  correction  has  been  noted 
in  the  list  of  parts  (p.   142)  for  the  article  "A  Good 
Amplifier-Power  Unit  for  the  250  Tube"  The  Dongan  Con- 
denser Unit,   Ci,   is   listed   at   $16.50,   instead  of  $23.00,  as 
printed  in  the  list. 

—  WILLIS  KINGSLEY  WING. 


OOUBLEDAT,  DORAN  &  COMPACT,  INC.,  Garden  Qity,  J^ew 


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Copyright,  1928,  in  the  United  States.  Newfoundland,  Great  Britain,  Canada,  and  other  countries  by  Doubleday.  Doran  &  Company,  Inc.     All  right*  r«en*d, 

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122 


RADIO  BROADCAST  ADVERTISER 


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Lmazing  results  now  obtained  by  experimenters  with 
low-wave  reception  provide  real  thrills  for  the  radio 
fan.  The  new  Hammarlund  Plug-In  Coils  insure 
the  utmost  efficiency  in  low-wave  work. 

Secondary  and  tickler  are  space-wound  on  a  film  of 
high-test  dielectric  material.  Losses  are  low.  Re- 
sults are  exceptional.  A  set  of  three  coils  with  plug- 
in  base  (base  includes  variable  primary  coil  with 
flexible  phosphor-bronze  connections)  covers  the  20, 
40  and  80  meter  bands,  with  a  range  from  15  to 
107  meters.  Special  coils  available  for  higher  waves. 

Hammarlund  Low-  Wave  Inductors  for  R.F.  stages, 
using  either  standard  or  screen-grid  valves,  are  now 
also  provided  with  plug-in  base  for  convenient 
change  to  any  wave-length  from  15  to  107  meters. 
They  are  constructed  like  the  coils  described  above, 
without  tickler  or  variable  primary. 

The  remarkable  efficiency  of  the  new  screen-grid 
valves  is  further  increased  when  used  with  Hammar- 
lund No.  222  Coils,  specially  designed  for  screen- 
grid  circuits  covering  the  broadcast  range.  A  feat- 
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greatest  amount  of  coupling  consistent  with  selec- 
tivity required.  Only  two  inches  in  diameter,  they 
may  be  mounted  vertically  within  shields  or  other 
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PRODUCTS 


A  Giant  British  Radio- Equipped  Passenger  Airplane 


THIS  is  a  close-up  of  one  of  the  giant  DcHavilland  66 
Hercules  multiple-engined  airships,  fitted  with  three 
Bristol  Jupiter  450-horsepower  engines,  built  for  the  British 
Imperial  Airways  for  the  new  passenger  air  route  between 
England  and  India  via  Egypt,  Palestine,  Mesopotamia,  and 
Persia.  The  radio  cabin  is  the  most  spacious  yet  fitted  in  any 
airship  and  contains  the  best  apparatus  now  available. 


Under  the  new  international  aerial  regulations,  a  radio  oper- 
ator and  mechanic  is  carried  to  attend  to  the  apparatus  and 
operate  it.  Previously  the  radio  equipment  was  carried  in 
the  cockpit  and  operated  by  the  pilot.  The  power  of  the 
transmitter  is  150  watts.  The  set  is  slung  on  elastic  bands 
to  reduce  vibration;  the  wind-driven  generator,  minus  its 
propellor,  is  visible  just  under  the  top  wing 


124 


BEFORE  THE  BAIRD  "TELEVISOR" 

In  spite  of  the  miles  of  type  expended  on  television  it  is  not  yet  possible  by 
system  to  receive  ,mages  which  have  much  detail.    All  the  systems  known  are 
Simitar.  Although  it  ,s  possible  /or  expenmenters  to  construct  s.mple  rece.vers  to  p«rl(  up 
television  signals,  "u-henT  as,  and  if  transmuted,  the  results  are  d.tfcult  to  ach,eve.  The 
.Ilustrarion  shou*  Mrs.  Howe,  said  to  be  the  first  woman  whose  features  were     televised 
across  the  Atlantic  by  the  Baird  system 


Television? 


THE  promise  of  television  is  that  we  may 
see  events  as  they  occur,  no  matter  where 
we  are,  provided  we  have  a  television  re- 
ceiver and  provided,  also,  that  a  televisor  opera- 
tor is  present  at  the  event.  Televising  is  the 
broadcasting  of  images,  the  annihilation  of  dis- 
tance for  the  eye  as  aural  radio  has  done  for  the 
ear.  In  place  of  the  microphone  we  want  to  use 
the  camera  lens  together  with  some  device  that 
translates  light  reflected  from  the  object,  into 
electric  current  impulses  which  speed  to  our 
receiver  where  those  impulses  are  translated  back 
into  light  and  are  projected  on  a  screen 

This  is  the  promise  It  seems  so  simple.  Yet 
long  before  regular  braadcasting  of  programs 
commenced,  we  were  as  far  ahead  in  method  as 
we  are  now.  It  violates  no  confidence  to  say  that 
only  within  the  last  month  one  of  the  most  prom- 
inent workers  has  abandoned  the  problem  in 
favor  of  research  on  the  facsimile  transmission 
of  telegrams.  Another,  C.  Francis  Jenkins,  writes 
that  it  is  a  stubborn  problem  but  the  solution 
seems  to  be  right  around  the  corner.  In  England, 
Sir  Oliver  Lodge  raises  a  note  of  warning  against 
the  public  expecting  success,  stating  that  other 
scientists  are  in  accord  with  him.  Theodor 


By  R.  P.  CLARKSON 

Author  of  "The  Hysterical  Background  of  Radio" 


m 


EIGHTEEN  LINES  TO  THE  INCH 

This  drawing  shows  what  slight  modula- 
ation  is  required  to  portray  the  features. 
The  image  received  in  some  television 
outfits  is  no  larger  than  the  actual  size 
of  the  cut  above.  The  reader  may  imag- 
ine the  detail  of  the  received  picture 
where  the  image  of  an  entire  head,  for 
example,  must  be  included  in  this  space 

'25 


Nakken,  whose  researches  have  made  the  photo- 
electric tube  available  for  this  work,  states  flatly 
that  the  thing  is  impossible  with  the  methods 
now  being  tried,  except  at  enormous  costs.  With 
this  weight  of  authority  against  success,  let  us 
look  for  a  moment  at  the  problem. 

The  eye  is  a  camera,  but  a  very  defective  one. 
It  retains  an  impression  for  a  definite  period, 
normally  about  one-tenth  of  a  second,  and  be- 
cause of  this,  moving  pictures  are  possible.  On 
the  other  hand,  an  impression  must  affect  the 
eye  for  a  certain  definite  minimum  of  time,  de- 
pending upon  the  intensity  of  light,  or  it  won't 
register  in  the  consciousness  at  all.  This  makes 
possible  the  magician's  tricks  in  dim  light,  and 
makes  almost  impossible  the  achievement  of 
television. 

To  see  any  image  dot  by  dot,  the  first  essential 
is  that  the  eye  must  see  each  dot  for  a  period 
long  enough  to  awake  the  consciousness,  and  yet 
it  must  see  the  last  dot  of  the  image  before  the 
impress:on  of  the  first  dot  is  lost.  To  put  this  in 
figures  means  that  the  last  dot  must  be  shown 
within  a  tenth  of  a  second  after  the  first  dot,  and 
yet  each  dot  must  appear  for  at  least  the  five- 
hundred-thousandth  part  of  a  second,  strongly 


126 


RADIO  BROADCAST 


JULY,  1928 


BAIRD'S  FIRST  "TELEVISOR" 

This  crude  but  workable  apparatus,  undoubtedly  the  result  of  much  labor  on  the  part  of  Baird,  who, 
like  most  inventors  dependent  upon  their  own  resources,  had  very  little  money  with  which  to  carry 
on  his  experiments,  gives  an  idea  of  how  simple  is  the  essential  apparatus  required  for  the  production 
of  television  signals.  The  various  disks  function  to  break  up  the  object  to  be  transmitted  into  many 
tiny  dots  so  that  the  light  finally  reaching  the  photoelectric  cell  is  broken  up  into  many  consecutive 
impulses  each  of  which  corresponds  in  intensity  to  one  particular  spot  of  the  subject.  This  original 
model  has  been  placed  on  view  at  the  Science  Museum,  at  South  Kensington,  London 


illuminated.  These  two  figures  determine  the  size 
and  quality  of  the  possible  image.  They  indicate 
50,000  dots  to  the  picture  as  substantially  the 
possible  maximum  and  strong  artificial  illumina- 
tion as  essential  at  the  receiver,  unless  some  way 
is  found  to  maintain  the  illumination  of  the  dots 
beyond  the  period  of  their  stimulus. 

Transmitting  an  image  and  transmitting  a 
musical  composition  are  accomplished  in  the 
same  way.  The  music  is  sent  note  by  note  in 
ordered  sequence.  We  enjoy  it  as  it  is  produced. 
A  picture  is  similarly  subdivided  into  dots  of 
light  and  shade  and  these  dots  sent  in  any  se- 
quence, but  they  must  all  be  received  and  placed 
in  proper  relationship  before  there  is  any  picture. 
There  is  nothing  to  see  until  the  transmission  is 
ended.  In  telephotography,  time  is  no  bar  to 


transmission  because  each  dot  is  permanently 
recorded  as  received,  and  when  transmission  is 
ended  we  have  a  complete  record.  In  television, 
each  image  is  fleeting.  There  is  no  record.  It  is 
all  over  in  a  tenth  of  a  second  and  the  next  image 
is  on  the  way.  Time  is  of  the  essence  of  television. 
It  is  largely  the  problem  of  time  that  makes  suc- 
cessful telephotography  meaningless  with  respect 
to  television.  A  small  picture  sent  in  five  minutes 
is  commercially  perfect  but  to  send  3000  pictures 
of  the  same  size  in  the  same  length  of  time  is  an- 
other story. 

REQUIREMENTS   OF   A    GOOD    PICTURE 

XTEGLECTING  color  and  form,  for  the  mo- 
'  '  ment,  all  pictures  and  images  differ  from 
each  other  only  in  the  distribution  of  light  and 


shade.  The  range  of  light  intensities  is  of  the 
order  of  one  to  thirty,  as  we  go  from  deepest 
shadow  to  brightest  light.  But  all  these  intensities 
are  not  usually  sharply  defined.  They  may  shade 
into  each  other  abruptly,  however,  as  in  the  case 
of  a  church  steeple  standing  out  against  a  white 
cloud.  Draw  an  imaginary  line  across  the  steeple 
and  follow  in  your  mind  the  changing  light  and 
shade  along  that  line.  From  the  white  of  the 
cloud  you  may  change  suddenly  to  a  very  dark 
edge  of  the  steeple,  and  then  come  a  continual 
series  of  changes  through  all  shades  as  the  detail 
of  the  steeple  is  recorded.  Across  a  peaceful  land- 
scape even  greater  variations  may  be  found  as 
you  follow  a  straight  line  through  clouds,  trees. 
leaves  and  grasses,  flowers,  dirt,  stones,  pebbles, 
and  whatnot.  These  changes  in  light  and  shade 
are  the  "modulation"  of  the  picture. 

Long  experience  with  half-tones  has  shown 
that  to  produce  a  really  good  picture,  provision 
must  be  made  to  reproduce  130  to  150  changes 
in  light  and  shade  to  each  lineal  inch.  This  same 
modulation  may  be  required  up  and  down  a  ver- 
tical line  as  well  as  sideways  along  the  horizontal. 
In  other  words,  the  modulation  figure  for  a 
square  inch  may  be  of  theorderof  20,000  changes. 
If  the  figure  is  made  up  of  dots,  20,000  of  them 
have  to  be  printed  to  give  the  detail  of  a  fine 
half-tone.  On  cheap  news  print,  where  the  sur- 
face itself  is  rough,  as  low  as  2500  dots  per  square 
inch  are  used  in  the  poorest  of  newspaper  re- 
productions. Most  of  the  New  York  papers  use 
3969  dots  per  square  inch,  while  this  magazine 
and  other  popular  ones  on  good  paper  uniformly 
use  14,400  dots  to  the  square  inch.  Even  with 
the  highest  of  all  these  figures,  however,  details 
of  cloud  effects  cannot  be  reproduced  and  the 
beautiful  lights  and  shadows  of  woodcuts  are 
impossible. 

In  our  television  screen  image  let  us  aim  no 
higher  than  the  detail  of  a  news  print  photograph. 
For  each  square  inch  of  the  picture  there  must  be 
2500  dots  transmitted.  For  an  image  one  foot 
square,  which  wouldn't  give  much  of  a  view  of  a 
spectacle  such  as  a  ball  game,  there  would  be 
360,000  dots.  The  last  dot  must  arrive  within  a 
tenth  of  a  second  after  the  first  dot,  so  the  rate 
of  transmission  over  a  single  waveband  would  be 
3,600,000  dots  or  impulses  per  second.  Each  dot 
would  exist  only  that  small  fraction  of  a  second 


/Television  signals  from 
V  Radio  Receiver. 


Light 


Neon  Tube  lighted 
with  signals  from 
Receiver 

Revolving 
Lens  Disc" 


Output  to  Transmitter 
Antenna  system 


Image  produced  by 
light  from  Neon  Tube 
\ 


Slot  in 
Disc" 


Image  on  Translucent 
Screen 


Lenses 


BAIRD  S    TELEVISION    RECEIVER 

This  shows  the  arrangement  of  the  revolving  disc,  neon  tube  and  trans- 
lucent screen  used  in  one  model  of  the  Baird  television  receiver.  The 
light  from  the  neon  tube,  varying  in  accordance  with  the  picture  signals, 
passes  through  the  lenses  in  the  revolving  disc  (which  must  rotate  in 
synchrony  with  the  transmitting  apparatus)  which  focus  the  light  on  the 
screen;  the  image  is  viewed  from  the  opposite  side  of  the  screen.  The 
general  system  used  here  is  very  similar  to  that  used  by  Dr.  E.  F.  W. 
Alexanderson  of  the  General  F^lectric  Company  in  his  recent  demonstra- 
tion at  Schenectady.  The  only  difference  was  that  the  lenses  in  the  disc 
and  the  screen  were  dispensed  with  and  the  observer  saw  the  image  by 
looking  at  the  neon  tube  directly  through  the  revolving  disc.  The  received 
image  is  red  in  color — a  characteristic  of  all  television  reception  using 
neon  tubes,  with  their  characteristic  red  glow 


Shortwave/ 
Transmitter 


Subject 


THE    BAIRD       TELEVISOR 


This  transmitter,  the  result  of  experiments  by  J.  L.  Baird,  makes  use  of 
infra-red  rays,  invisible  to  the  human  eye,  but  capable  of  affecting  the 
photoelectric  cell  which  converts  the  varying  light  signals  into  corre- 
sponding electric  impulses.  The  infra-red  rays,  reflected  from  the  subject 
transmitted,  pass  through  the  cellular  structure  which  breaks  up  the 
light  into  many  small  sections  or  dots.  The  light  then  passes  through  the 
two  revolving  discs  which  rotate  in  such  a  manner  as  to  expose  to  the 
light-sensitive  cell  at  any  moment  only  one  of  the  light  beams  from  the 
cellular  structure.  The  resulting  electric  impulses  are  then  caused  to 
modulate  the  radio  transmitter.  The  use  of  infra-red  rays  is  not  essential 
to  the  operation  of  this  camera.  Electrically,  the  system  will  function 
satisfactorily  with  any  type  of  rays  to  which  the  photoelectric  cell  will 
respond.  The  amount  of  illumination  required  is  quite  intense,  however, 
and,  if  ordinary  lights  were  used,  one  would  not  be  able  lo  endure  the 
intense  glare  for  very  long 


JULY,  1928 


WHAT  HOPE  FOR  REAL  TELEVISION? 


127 


and  would  obviously  never  register  on  the  eye 
unless  it  happened  to  be  repeated  in  successive 
pictures,  and  possibly  not  then.  It  would  be  so 
repeated,  of  course,  unless  motion  had  ensued  in 
the  intervening  tenth  of  a  second  If  there  had 
been  motion  that  part  of  the  picture  would  be 
blank.  This  is  the  first  difference  we  find  between 
motion  pictures  and  television.  In  the  movies  we 
see  a  blow  start  and  see  the  arrival  of  the  fist. 
We  imagine  the  rest  of  it  just  as  we  see  the  suc- 
cessive positions  of  a  speeding  automobile  and 
imagine  the  continuity.  Only  by  speeding  up  the 
camera  to  get  intervening  snaps  and  presenting 
them  in  slow  motion  do  we  get  detail.  Bach  com- 
plete picture  flashes  at  once.  In  television,  be- 
cause of  subdivision  into  dots,  only  one  dot  is 
shown  at  a  time  and  the  mind  will  not  retain 
this  short  flash  during  the  remainder  of  the  pic- 
ture. We  must  make  the  screen  retain  the  dot 
for  us. 

A  second  distinction  comes  from  the  fact  that 
we  cannot  enlarge  the  picture  received  in  tele- 
vision with  any  increased  detail  in  the  result. 
We  have  chosen  the  minimum  number  of  dots 
per  square  inch  to  give  a  passable  image.  If  this 
is  enlarged  by  a  projecting  lens,  we  simply  sepa- 


48  times  each  second, arm  energizes 
50  segments  across  one  ro*,2500 
segments  excited  18  times  each  second 
gives  45.000  light  images  per  second 


AnooV  Ctthode 


'-Lei* 


'-Wire  to  Grid  of 
Transmitting  Amplifier 


CAMERA  CATHODE   RAY  OSCILLOGRAPH 

THE  SWINTON-CLARKSON  TELEVISION 

CAMERA 

I  n  this  device  the  person  or  object  to  be  televised 
is  located  in  front  of  the  lens,  the  lens  func- 
tioning to  focus  the  reflected  light  from  the  ob- 
ject onto  the  plate.  A  stream  of  electrons  from 
the  cathode  is  attracted  to  the  positively 
charged  anode  and  a  great  many  of  the  electrons 
pass  through  the  hole  in  the  anode  plate  and 
reach  a  group  of  photoelectric  cells.  In  passing 
through  the  space  between  the  hole  in  the  anode 
and  the  plate  the  electrons  come  under  the 
influence  of  the  two  coils  A  and  B;  coil  A  causing 
the  stream  to  be  deflected  up  and  down  the 
plate  and  coil  B  causing  the  stream  to  move 
back  and  forth  across  the  cells.  The  image  on 
the  plate  is  scanned  in  this  manner 


rate  the  dots.  If  we  magnify  the  size  ten  times 
we'll  have  only  250  dots  per  square  inch  and  only 
at  a  distance  will  this  give  the  effect  of  a  photo- 
graph. We  haven't  even  the  value  of  a  printed 
half-tone  where  the  dots  are  of  varying  size  and 
shape  as  well  as  shade.  Our  dots  are  uniform  ex- 
cept in  shade.  This  may  be  overcome  by  the 
screen  in  the  device  described  later. 

Now,  getting  back  to  the  3,600,000  impulses 
per  second.  This  is  equivalent  to  the  modulation 
frequency  in  aural  radio.  The  minimum  fre- 
quency of  the  carrier  would  be  about  ten  times 
that,  or  a  frequency  of  36,000  kilocycles,  approx- 
imately eight  meters.  A  larger  picture  or  a  better 
picture  would  drive  us  down  to  still  shorter 
waves. 

A    FOUR-INCH    SQUARE    IMAGE 

CUPPOSE,  instead  of  a  foot  square,  we  make 
*^  the  image  four  inches  square.  Even  this 
would  mean  40,000  dots  for  each  picture  or 
400.000  impulses  per  second.  Our  carrier  max- 
imum would  be  75  meters.  Even  suppressing  one 
side  band,  the  400,000  modulation  frequency 


Incoming  "Image"  signals 
from  Photo -Electric  cells 
at  sender 


calls  for  a  receiver  to 
amplify  evenly  over  a 
band  of  400  kilocycles 
or  as  much  as  40  of  our 
present  broadcast  chan- 
nels. This  is  for  a  tiny 
picture  of  poor  quality 
and  minimum  speed.  For 
any  fast  event,  for  a 
larger  picture,  or  for 
even  newspaper  quality, 
what  a  complex  receiver 
must  be  devised!  One 
such  station  would  blan- 
ket the  entire  broadcast 
spectrum. 

Go  down  in  size  and 
quality,  if  you  will.  A 
three-inch  square  pic- 
ture with  2  5  modulations 
to  the  lineal  inch  or  625 
dots  to  the  square  inch, 
means  only  56,250  im- 
pulses per  second.  The 
carrier  could  be  as  high 
as  535  meters  but  our 
tuning  and  amplifica- 
tion would  be  over  five 
channels  10,000  cycles  wide.  To  get  within  the 
legal  separation  of  stations  we  can  use  a  modula- 
tion of  only  5000  impulses  per  second  which,  for 
a  barely  recognizable  image,  would  give  us  only 
one  square  inch,  remembering  that  we  must  send 
10  pictures  a  second. 

What,  then,  is  Baird  in  England  doing,  for 
example?  Obviously  the  only  thing  he  can  do 
and  basically  the  only  thing  that  has  ever  been 
done  in  television.  That  is,  to  select  as  the  object 
to  be  televised,  something  that  has  few  grada- 
tions of  light  and  shade  and  extremely  slow 
movement.  This  is  the  human  face.  It  is  a  fami- 
liar object,  almost  entirely  white  space  with  the 
shadows  around  eyes  and  nose  very  ill  defined 
and  their  outline  of  no  particular  importance  in 
recognition.  The  cartoonists  have  taught  us  that 
we  need  nodetail  of  afaceto  recognizethe  person. 
There  is  always  some  outstanding  characteristic 
that  suffices.  Slight  blurring  would  rather  soften 
the  result  instead  of  spoiling  it. 

Television  is  not  achieved  merely  because  see- 
ing faces  at  a  distance  has  been  and  will  be  ac- 
complished. It  was  in  recognition  of  this  fact  that 
the  English  publication  Popular  Wireless  un- 
successfully sought  to  induce  Baird  to  televise 
a  simple  cube  in  slow  motion  to  win  the  sum  of 
§5000  that  magazine  offered.  That  Baird  ignored 
the  challenge  must  merely  mean  that  he,  too, 
recognizes  the  limitations  of  his  apparatus. 

There  are  other  problems  besides  that  of  time 
in  its  relation  to  the  defects  of  vision.  There  is 
the  question  of  synchronizing  the  mechanically 
moving  parts  of  transmitter  and  receiver.  When 
things  happen  in  the  hundred-thousandth  part 
of  a  second,  there  is  need  for  absolute  accord  on 
both  ends  of  the  line.  If  the  same  power  line  is 
available  at  both  ends,  synchronous  motors  may 
be  kept  in  step,  but  this  exists  only  in  few  local- 
ities and  over  short  distances.  Synchronizing  by 
this  means  it  is  not  a  real  solution  of  the  problem. 

THE    REAL    DIFFICULTY 

AS  THIS  brief  review  indicates,  the  real  draw- 
back is  the  fact  that  the  picture  must  be 
subdivided  and  sent  as  a  sequence  of  impulses. 
We  would  face  similar  difficulties  with  sound 
broadcasting  if,  for  example,  we  had  to  send  the 
whole  of  an  opera  selection  as  one  blare  of  noise 
in  3  tenth  of  a  second.  It  could  be  done,  of  course, 
by  securing  a  sufficient  number  of  musicians  so 
that  each  need  sound  but  one  note.  Then,  at  a 
given  signal,  every  musician  in  this  enormous 


Neon  Gas-. 


Potential  sufficient  to 
cause  Neon  Gas  to  glow 


THE    BELL   TELEPHONE    LABORATORIES 

TELEVISION    RECEIVER 

A  large  neon  tube  forms  the  basis  of  this  television  receiver.  On  the  back 
side  of  the  tube  2500  segments  of  tin  foil  are  cemented,  connecting  by 
means  of  individual  wires  to  2500  segments  on  the  commutator,  which 
revolves  in  synchrony  with  the  apparatus  at  the  transmitter.  The  incom- 
ing signals,  modulated  in  accordance  with  the  shading  of  the  subject  being 
transmitted,  are  amplified  and  cause  segments  of  the  neon  tube  to  glow 
with  a  brilliancy  dependent  upon  the  shading  of  the  subject  being 
transmitted 


orchestra  would  sound  his  note  and  go  home.  We 
would  receive  the  opera  selection  but  it  would 
hardly  be  worth  while.  Yet  this  is  exactly  what 
the  eye  demands  in  television. 

One  thought  has  been  to  divide  the  object  into 
units.  That  is,  in  terms  of  pictures,  not  to  send 
the  whole  picture  over  one  carrier  but,  in  effect, 
send,  say,  144  pictures,  each  an  inch  square,  and 
at  the  receiver  these  would  make  up  into  a  single 
image  one  foot  square.  This  was  one  of  the  first 
ideas  suggested  as  long  ago  as  1880.  Carried  to 
its  extreme,  perfect  results  would  be  achieved 
but,  within  the  limits  of  costs  and  apparatus,  we 
merely  multiply  our  troubles.  Sixteen  pictures 
3  inches  square  might  be  managed  if  we  could 
send  anything  but  a  crude  3-inch-square  picture. 
It  would  be  at  16  times  the  cost  and  16  trans- 
mitters as  well  as  16  receivers  would  be  needed 
and  all  would  have  to  be  synchronized.  Along 
similar  lines  was  Doctor  Alexanderson's  bundle 


Coil  A 


Perforated  Stop  Plan 
:with  fixed  opening 


-B 


Defecting 
Plate 


Wire  from  ,  - 

Receiver  Amplifier 


CAMPBELL    SWINTON    TELEVISION 

PROJ  ECTOR 

This  television  projector,  sometimes  called  a 
television  receiver,  uses  an  arrangement  similar 
to  that  incorporated  in  the  Campbell  Swinton 
camera  suggested  in  1908.  The  electron  stream 
from  the  cathode  is  caused  to  scan  the  fluorescent 
screen  due  to  the  action  of  the  coils  A  and  B, 
their  intensity  being  varied  by  means  of  the  two 
deflecting  plates.  Potential  from  the  receiver  am- 
plifier is  impressed  on  the  deflecting  plates  and 
causes  the  number  of  electrons  passing  through 
the  opening  in  the  stop  plate  to  vary  in  accord- 
ance with  the  image  signals  from  the  transmitter. 
The  screen  at  the  left  of  the  camera  becomes 
fluorescent  under  theaction  of  the  electron  stream 
and  the  image  then  becomes  visible  to  any  one 
standing  in  front  of  the  screen 


128 


RADIO  BROADCAST 


JULY,  1928 


CAMERA 


P  and  Fare  the 
elements  of  a  special 
two  electrode 
Vacuum  Tube 


THE    CLARKSON    TELEVISION    PROJECTOR 

This  projector  makes  use  of  a  three-electrode  tube,  the  grid  of 
which  functions  to  control  the  electron  stream  from  the  filament 
F.  The  electrons  passing  through  the  opening  in  the  plate  P  are 
caused  to  scan  the  screen  due  to  the  action  of  the  two  coils  A 
and  B.  A  phosphorescent  screen  (rather  than  a  fluorescent  screen) 
is  used  so  that  the  screen  will  continue  to  glow  for  an  interval 
after  the  impulse  stimulus' is  removed.  This  results  in  consider- 
able improvement  for  it  reduces  the  amount  of  light  required 
and  also  permits  the  use  of  a  greater  number  of  impulses  so  that 
greater  detail  may  be  obtained 


of  seven  light  rays  analyzing  the  object,  instead 
of  one,  and  Doctor  Ives'  experiment  with  sub- 
divided photoelectric  cell  and  screen. 

The  Englishman,  A.  A.  Campbell  Swinton,  in 
a  letter  to  Nature,  June  18,  1908,  and  more  in  de- 
tail in  his  Presidential  Address  to  the  Rontgen 
Society,  November  7,  1911,  set  forth  the  genesis 
of  an  idea  along  these  lines  but  one  never  given 
publicity  and  never  tried  out.  I  have  taken  the 
liberty  of  modifying  this  idea  and  present  it 
herewith  as  a  last  desperate  hope. 

IS   THIS   THE    WAY   OUT? 

IN  ALL  other  television  devices  before  the  pub- 
'  lie  at  present  the  method  of  telephotography 
is  being  used,  speeded  up  to  the  tenth-second 
requirement.  At  the  transmitter  is  a  photoelectric 
cell.  A  beam  of  light  explores  the  object  to  be 
"televised"  and  is  reflected  to  the  cell.  This  cell 
modulates  the  carrier  wave,  just  as  though  it 
were  a  microphone.  Varying  light  actuates  it 
just  as  varying  sound  actuates  the  microphone. 
At  the  receiver,  in  place  of  the  loud  speaker,  is  a 
glow  lamp — usually  a  neon  tube  in  one  form  or 
another — which  changes  its  brilliancy  in  step 
with  the  received  impulses  from  the  photoelec- 
tric cell.  The  light  from  this  lamp  is  made  to 
explore  a  screen  in  synchronism  with  the  beam 
at  the  transmitter.  The  usual  method  of  swinging 
the  beams  of  light  up  and  down  and  over  the 
object  and  screen,  is  a  mechanically  revolving 
disc  perforated  spirally  with  holes,  a  device  pa- 
tented by  Nipkow  in  1884,  this  inventor  being 
the  first  to  see  the  advantage  of  breaking  up  a 
picture  into  lines. 


In  the  Swinton  method  there 
is  no  mechanically  moving  part. 
The  object  is  illuminated 
strongly  and  we  have  a  "televis- 
ion camera,"  let  us  say,  which 
projects  the  image  to  be  trans- 
mitted, not  on  a  film,  but  on  a 
composite  plate  made  of  tiny 
cubes  of  photoelectric  material 
insulated  from  each  other.  The 
camera  is  gas  tight  and  filled  with 
sodium  vapor,  which  conducts 
negative  electrons  more  readily 
under  the  influence  of  light.  Be- 
tween the  projecting  lens  and 
the  composite  plate,  in  the 
vapor  chamber,  is  a  gauze  wire 
screen.  The  charge  on  this  gauze 
screen  modulates  the  transmit- 
ting tube. 

In  effect,  the  gauze  screen 
is  connected  by  radio  to  a  plate 
in  the  receiver  projection  appa- 
ratus. A  beam  of  cathode  rays  is 
directed  past  this  plate  towards 
a  sensitive  fluorescent  screen. 
Only  when  the  rays  are  slightly 
bent  by  the  repulsion  of  the  plate 
can  they  pass  through  a  fixed 
opening  and  actually  be  directed 
to  the  fluorescent  screen  to  cause 
a  luminous  spot. 

At  the  transmitting  end  there 
is  also  a  cathode-ray  beam  continually  searching 
the  composite  plate  of  the  camera  but  on  the 
back  side  from  where  the  image  illuminates  it. 
As  this  stream  strikes  each  little  photoelectric 
cube,  it  charges  it  negatively  but  the  charge  is 
dissipated  unless  that  cube  is  illuminated  on  the 
front  by  light  from  the  object.  In  the  latter  case, 
the  charge  of  the  cube  will 
pass  away  through  the  ionized 
vapor  along  the  illuminating 
beam  of  light  until  it  reaches 
the  gauze  screen,  whereupon 
that  charge  becomes  an  im- 
pulse carried  over  to  the  re- 
ceiver projection  apparatus 
where  it  charges  the  deflect- 
ing plate  which  bends  the 
synchronized  cathode  ray  so 
that  a  luminous  spot  is  formed 
on  the  fluorescent  screen. 

Each  received  impulse  must 
correspond  in  position  to  the 
illuminated  cube  of  the  com- 
posite plate,  requiring  the  syn- 
chronizing of  the  two  cathode 
ray  beams.  This  may  be  done 
at  each  end  separately  through 
the  same  construction  as  the 
cathode  ray  oscillograph,  the 
beam  being  moved  by  the  mag- 
netic field  of  two  coils  at  right 
angles  to  each  other  and  hav- 
ing widely  differing  frequencies 
as  10  and  1000  cycles  or  10  and 
10,000  cycles.  Substantially 


the  two  rays  are  merely  tracing  curves  of  great 
amplitude  and  rather  low  frequency. 

In  this  method  the  object  itself  is  not  explored 
but  its  projected  image  is  automatically  sub- 
divided by  the  composite  plate  of  the  camera, 
which  has  no  electrical  connections.  Only  one 
carrier  wave  is  required  but  we  still  have  the 
broad  band  of  frequencies  to  detect  and  amplify 
at  the  receiver.  No  mechanically  moving  parts 
are  used.  A  telephoto  lens,  a  wide  angle  lens  or 
any  usual  camera  arrangement  may  be  used  at 
will.  Synchronizing  presents  no  difficulties  and 
the  method  is  as  adaptable  to  wire  as  to  radio. 
But  as  yet  it  has  not  been  found  practical,  the 
main  reason  being  that  the  use  of  photoelectric 
material  in  the  composite  plate  means  that  elec- 
trons will  be  given  off  continually  as  long  as  light 
falls  on  the  plate,  and  in  mass  when  the  image 
shifts. 

In  the  writer's  proposed  modification  of  the 
Swinton  device,  the  material  of  the  composite 
plate  is  non-photoelectric  but  conductive.  The 
writer  uses  a  closed  electric  circuit  of  which  the 
exploring  electron  beam  is  a  part,  the  conductive 
cube  is  a  part  when  the  beam  strikes  it.  and  the 
ionized  path  in  the  vapor  is  the  varying  part  of 
the  circuit.  An  amplifying  tube  is  readily  coupled 
to  this  circuit. 

In  the  projector  proposed  by  the  writer,  he 
suggests  the  use  of  a  three-electrode  vacuum 
tube,  using  a  heavily  biased  grid,  the  incoming 
signal  modulating  that  grid,  as  usual,  and  per- 
mitting the  flow  of  an  electron  beam.  The  ob- 
serving screen  must  be  phosphorescent,  instead 
of  fluorescent.  That  is,  it  must  glow  for  a  time 
after  the  impulse  strikes  it. 

If  any  method  within  our  knowledge  has  possi- 
bilities, this  is  it.  If  it  fails,  television  will  await 
the  genius  who  conceives  some  new  way  of  break- 
ing up  an  image.  There  is  no  other  hope. 


L 


P,G  and  F  are  the  elements 
of  a  special  Vacuum  Tube 


THE  CLARKSON  TELEVISION  CAMERA 
In  this  arrangement  a  closed  electric  circuit  exists  from  the  source 
of  electrons  F  through  the  beam  of  electrons,  which  act  as  a 
flexible  conductor,  to  any  conductive  member  of  the  non- 
photoelectric  composite  plate,  through  the  plate  to  the  wire 
gauze  screen,  along  the  screen  to  the  coupling  resistance  and 
back  to  the  filament  circuit.  The  object  to  be  televised  stands 
in  front  of  the  lens  at  the  left 


IMh.W.N    AND    IIMimPKMAHQN    OK  IlKKHVI     KAniQ    KVUM  1  N 

Aviation  Must  Come  to  the  Use  of  Radio 


THE  question  of  wireless  received  serious 
consideration,"  wrote  Commandant  James 
C.  Fitzmaurice  in  the  New  York  Times, 
after  the  first  westward  airplane  flight  across 
the  Atlantic,  "but  it  was  decided  that  an  ef- 
ficient and  useful  wireless  set  would  weigh  ap- 
proximately 180  pounds.  It  was  decided  that 
this  weight  of  benzol  would  be  better.  This  was 
the  one  weak  point  in  the  organization  of  the 
flight,  as  we  now  realize  that  had  we  had  a  wire- 
less set  on  board,  upon  our  estimated  arrival  in 
the  neighborhood  of  Newfoundland,  we  could 
have  been  given  almost  our  exact  position  by 
the  direction-finding  stations  along  the  coast 
and  informed  of  the  precise  direction  and  veloc- 
ity of  the  wind  over  the  area,  and  we  would  have 
made  New  York  easily  and  accomplished  our 
objective.  We  consider  wireless  absolutely  neces- 
sary for  all  future  undertakings  of  this  nature." 

If  radio  could  have  enabled  the  German  fliers 
to  reach  their  goal,  it  may  be  argued  with  equal 
force  that  Nungesser,  Coli,  Hinchcliffe,  Hamil- 
ton, St.  Roman,  and  the  other  transatlantic 
fliers  might  well  have  made  safe  landings,  guided 
through  the  hazardous  Newfoundland  region 
by  compass  bearings  from  Cape  Race,  Belle  Isle, 
and  Chebucto  Head.  Had  the  Bremen  been 
properly  equipped  with  radio,  she  would  have 
landed  in  an  airport  and  Floyd  Bennett's  tragic 
flight  to  aid  the  German  aviators  would  have 
been  unnecessary.  Last  year,  the  Bremen  started 
a  westward  flight  across  the  Atlantic  but, 
warned  by  radio  of  unfavorable  weather,  re- 
turned to  safety.  Byrd's  transatlantic  flight  was 
successful  largely  because  of  radio  beacon  sig- 
nals although  he  did  not  make  the  most  of  his 
installation.  Those  who  attempt  long-distance 
flights  without  the  aid  that  radio  can  give  them, 
heroes  or  not,  are  both  unscientific  and  fool- 
hardy. The  fact  that  some  succeed  in  their 
undertaking  without  radio  is  no  justification  for 
recklessness. 

Only  when  transatlantic  and  international 
flights  become  common  and  scheduled  occur- 
rences will  long-distance  flying  take  its  place 
among  the  useful  arts  of  human  society.  Like 
radio,  aviation  must  become  a  regular  service 
which  is  expected  to  function  satisfactorily  and 
without  failure. 

The  scientific  development  of  aeronautics  has 
already  advanced  to  the  point  where  we  have 
aircraft  and  aircraft  motors  which  are  entirely 
serviceable  and  reliable.  Ships  can  be  built  to 
meet  almost  any  reasonable  requirement.  Mo- 
tors are  still  uneconomically  shortlived,  but 
their  limitations  are  so  well  known  that  an 
ample  factor  of  safety  for  any  reasonable  flight 
can  be  provided. 

The  principal  obstacles  to  everyday  use  of 
aviation  are  safety  and  cost.  When  the  problem 
of  safety  is  solved,  the  public  will  so  quickly 
accept  the  airplane  as  a  means  of  rapid  travel 
that  the  cost  of  flights  will  fall  to  a  point  jus- 
tified by  the  time  which  they  save.  Public  con- 
fidence, based  on  reliable  service,  rather  than 
spectacular  feats,  is  the  greatest  need  of  avia- 
tion. 

The  development  of  radio  communication  as 
an  integral  part  of  our  commercial  flying  struc- 


ture is  the  most  important  and  the  most  neg- 
lected step  to  promoting  safety  in  aviation.  Its 
general  adoption  is  not  so  much  a  matter  of 
developing  new  equipment  as  one  of  convincing 
the  aircraft  industry  of  the  value  of  radio. 

Radio  serves  the  aeronaut  in  several  distinct 
capacities.  At  all  important  landing  fields,  radio 
stations  are  required  for  the  exchange  of  weather 
reports,  to  report  the  leaving  and  arrival  of 
ships,  to  issue  orders  to  aircraft  in  flight  and  to 
disseminate  periodic  weather  reports.  With  a 
properly  coordinated  system  of  collecting  and 
distributing  weather  information,  storm  warn- 
ings can  be  issued  in  ample  time  to  assure  the 
comfort  of  passengers  and  the  safety  of  cargo. 
At  least  500  low-power  transmitting  stations  for 
this  purpose  will  ultimately  be  required,  as  well 
as  a  few  high-power  transmitters  to  broadcast 
information  to  these  landing  field  stations. 

Another  important  function  of  radio  is  to 
mark  out  the  highways  of  the  air  and  to  keep  the 
aviator  on  his  course.  The  aircraft  direction 
beacon,  which  radiates  two  directional  signals  at 
forty-five  degrees  from  the  prescribed  course, 
has  demonstrated  its  usefulness.  The  radiated 
signals  consist  of  mechanically  sent  dots  and 
dashes,  so  timed  that,  when  a  flier  is  exactly  on 
his  course,  the  combined  signal  received  from 
both  directional  stations  equally  forms  a  single 
series  of  dashes.  But  should  the  pilot  deviate 
from  his  course,  the  signal  from  one  of  the  direc- 
tional antennas  predominates  and  produces  a 


ABOARD    A    PRIVATE    MOTOR    YACHT 

The  motor  yacht  Crusader,  owned  by  A.  K' 
Macomber  of  California  is  one  of  the  most  elab- 
orately fitted  yachts  afloat,  from  the  radio 
point  of  view.  The  ship  has  elaborate  broadcast 
receiving  equipment  with  loud  speaker  outlets 
in  nearly  every  cabin.  The  illustration  shows  the 
o.;-kw.  voice  transmitter  aboard  the  Crusader 

129 


distinctive  signal,  enabling  him  to  determine 
whether  the  plane  is  to  the  right  or  to  the  left 
of  the  prescribed  course.  At  a  distance  of  more 
than  fifty  miles,  short-wave  beacons  become 
erratic  in  their  behavior  and  directional  readings 
unreliable.  Therefore  aircraft  direction  beacons 
should  be  placed  in  operation  each  one  hundred 
miles  along  the  principal  highways  of  the  air. 

A  third  service  is  the  aircraft  beacon  or  radio 
lighthouse  which  gives  a  distinctive  signal  to  a 
ship  in  flight  when  it  is  within  a  definite  distance 
of  a  given  marker  point.  In  foggy  and  heavy 
weather,  the  radio  beacon  enables  the  flier  to 
come  sufficiently  close  to  the  landing  field  that 
its  neon  light  beacon  can  guide  him  to  a  safe 
landing.  Literally  thousands  of  these  low-power 
marker  beacons  are  required  to  serve  as  the  sign 
posts  on  the  highways  of  the  air. 

Recently,  the  Department  of  Commerce 
awarded  a  contract  covering  radio  equipment 
for  twelve  radio-controlled  stations,  six  radio 
beacons  and  twelve  markers,  at  a  total  cost  of 
slightly  more  than  $150,000.  The  Assistant 
Secretary  of  Commerce  for  Aeronautics,  William 
P.  MacCracken,  stated: 

"Radio  telephone  communication  to  the  air- 
plane is  expected  materially  to  decrease  acci- 
dents and  provide  for  stability  of  schedules 
with  greater  comfort  to  air  travelers  and  may 
be  considered  the  greatest  need  of  air  trans- 
portation to-day." 

The  leaders  of  research  in  the  radio  industry 
have  by  no  means  neglected  the  requirements  of 
aviation.  The  General  Electric  Company  and 
the  Westinghouse  Company  have  developed 
standard  models  of  directional  signal  transmit- 
ters and  beacon  equipment.  The  American 
Telephone  &  Telegraph  Company  has  recently 
added  an  airplane  to  its  experimental  equipment 
at  \\  hippany  in  order  to  perfect  various  types  of 
aircraft  radio-communication  apparatus.  Re- 
ceivers which  give  visual  indication  of  direction 
have  been  developed. 

The  principal  obstacle  to  the  use  of  radio  on 
aircraft  arises  out  of  the  fact  that  radio  is  con- 
sidered by  the  greater  number  of  pilots  only  as 
an  additional  burden  and  nuisance.  The  airmen's 
opposition  is  singularly  reminiscent  of  the  ridi- 
cule which  sea  captains  accorded  radio  when 
the  first  installations  were  being  made  on  pas- 
senger ships.  It  required  more  than  a  decade  of 
education  to  make  the  sailor  welcome  the  radio 
operator.  The  aircraft  pilot  remembers  radio  as  a 
necessary  evil  to  his  course  in  military  flying. 
He  complains  of  the  radio  helmet  which  he  must 
wear,  because  it  prevents  him  from  hearing  the 
functioning  of  his  motors.  His  ear  must  be  ever 
alert  to  observe  the  slightest  irregularity  in  their 
functioning.